I hate the idea - mainly for story reasons. Most of the new co-op zones are bad enough with non-specific villain content.
Villains need more machiavellian schemes and dirt evil tasks as befits their Destined One/Arachnos status, not to be the sidekick of some cowl-clad fool 
Ouroboros had the best split so far - pitting heroes and villains against each other in a similar fashion. Same with the Midnighters Club.
Cimerora is okay, though the motivation for villans to assist should be a bit more compelling earlier on...
It'd be nice if we could get a co-op zone where Heroes would have to help the Villains out 'for the greater good', rather than the usual 'villains doing the right thing'.
The closest to this type of mission is "The Fall of the 5th" Ouroboros mission, wich is a shame isn't actually co-op, since the hero version is the same as the villain version.
I really should do something about this signature.
there are often cases in comic books where heroes have to team up with vilains to achieve a goal, however, invariably the villain has an ulterior motive.
I think co-op missions should have an element of this.
for example:
a mission to stop a mad scientist from creating a legion of super soldier cyborgs:
The Evil Scientist Dr. mania has gone too far. Arachnos and Longbow agree that he must be prevented from achieving his goals to create a nemesis/clockwork hybrid in his efforts to create a new super soldier. Your mission is to take part in a joint task force to discover Dr. Mania's hideout and put a stop to his plans. As a joint task force you will be working with members from both camps.
mission 1: Alert! Dr. Mania's minions have been spotted in Cap Au Diable power plant:
get to Cap Au Diable: all heroes will be issued with an Arachnos ID allowing them entry to the rogue isles. Find out what they are doing in the power station.
side objective for heroes: Recover satellite imagery data disk : a few months ago a surveillance satellite crashed in the sea near cap au diable but before Longbow could get there the satellite was salvaged. Now the locator on the data matrix has been activated and appears to be somewhere within the power facility. Recover the data matrix.
At a random point in the map there will be a glowy. if a villain recovers the glowy, the recoverer gets some XP and some inf (as a reward for turning it over to the authorities). If a hero collects it , all heroes on the mission get inf/xp/prestige.
Side effect: a random amount of days later, a longbow assult party will attack a random zone in the rogue isles.
mission 2: reports in of Mania's forces in IP:
Mania sent a task force into IP using a stolen Arachnos Submarine. It appears to have surfaced beside an IP processing plant. find out what they are doing and stop them. Villains will be issued with ID to allow them access under hero supervision only.
Villain Side mission: recover recording of Lusca song: same as first, a glowy.
if villains succeed, arachnos manage to re-create the lusca song and a random amount of time later the giant octopus attacks a random Paragon zone that has water. (IP , Talos, FF , PI etc). Of course, this is dependant on Lusca actually attacking stuff and not just sitting there.
etc. until finally:
objective: both: stop Dr. Megal o'Mania defeat AV + Guards
Objective heroes 1: destroy Mania's plans
Objective Villain 1: retrieve Mania's plans
if heroes succeed: xp bonus + random recipe (pool a or b) + release codes sent to clockwork captive in rogue isles: sparks a clockwork invasion as they go for revenge
If villains succeed: xp bonus + recipe + modified goldbrickers attack random coastal Paragon zone
Objective heroes 2: take villains into custody with data tag
Objective villains 2: tag heroes for transport to interrogation cells
each participant is given a 1 use temporary power that can be used on any ally (hero or villain). it has long activation time during which time the user cannot move. if the victim moves out of sight the power fails and is wasted, if interrupted the power fails and is wasted.
effect: next time the hero or villain is defeated and goes to hospital or base , or next time the character uses teleportation systems other than travel power, they are shunted to a holding facility instead where they must escape from.
once the victim shows up the person that tagged him or her is rewarded with a recipe and a prestige bonus.
each character can only ever have one tag active at any time and if given the tag power again, can opt to cancel the old tag.
Note: the tagging does not appear on combat statistics so it is possible for a hero or villain to manage it without being noticed.
Note also: teleport powers are only shunted once the task force is finished.
[ QUOTE ]
Villains need more machiavellian schemes and dirt evil tasks as befits their Destined One/Arachnos status, not to be the sidekick of some cowl-clad fool
[/ QUOTE ]
Heroes may not enjoy working with evil types too 
And it's also harder to create evil missions, because major Villain successes would alter the game world, whereas major Hero successes preserves what we have.
@Golden Girl
City of Heroes comics and artwork
I love the coop zones too, those chicken mobs are awesome.
What?
[url=http://vox-doom.deviantart.com]Take A Gander At This.[/url]
¬_¬ Vox, just ¬_¬
I love co-op zones and co-op TFs, but hate the idea of existing hero-only or villain-only TFs/SFs being changed to co-op without a story rewrite. Are you seriously suggesting that heroes would want to go on an LRSF to take down the Freedom Phalanx? That kind of thing would get your hero licence revoked by Freedom Corp 
We just need more co-op zones/TFs - and really there is no major stretch of logic needed if the Devs do it right. Just like heroes/villains combine forces in the Marvel universe to fight off Galactus and similar planetary threats, we just need more global threats here that threaten the existence of Earth (i.e. both Paragon and the Rogue Isles under threat). I'm sure the "Coming Storm" storyline will culminate in such a threat, and the Rikti storyline does too, but the lore of the game has several factions that both heroes/villains would be eager to stop and willing to co-operate to do so (and no, I don't just mean Nemesis):
1) The Banished Pantheon gods could be brought back (Dark Astoria co-op revamp)
2) Merulina, the Coralax's alien goddess, could awaken (new underwater zone)
3) Rularuu could escape the Shadow Shard,
4) Reichsman, the Nazi Statesman from an alternate universe, could be brought back with a world-threatening scheme (Boomtown revamp, as he's supposed to be in stasis under the rubble of the Freedom Phalanx base there)
5) The Devs could invent new world-devouring/destroying threats from space or other dimensions
i like to see a WW 1 or 2 as s co-op zone, there has been alot of comics or superheroes cartoons where this has happen. of course we know who won already but it still could be tossed in due to the fact that someone from the future went back to over powering tech from the future that could change the past..... oh well here hoping
The 5th Column seem to use time travel a lot, so it's quite likely they'd try and go back and "fix" the outcome of the war.
@Golden Girl
City of Heroes comics and artwork
I love the Coop zones and, most of the people I have been teaming with, all of them love playing in the Coop zones too. Sadly, though, we only have 2: Rikti war zone and Cimeroma; and 2 sets of TFs/SFs, one in each.
I do feel that most people would want to see more Coop zones and more join operations (missions) between Hero and Villain ATs. I understand that it takes a bit of effort to develop a new zone. So how about allowing Hero to do Villain's SF and vice versa?
I have once read about the 'Going Rogue' suggestion either in this or the US forum - but I have not keep up-to-date with that line of suggestion anymore. Perhaps something along similar line of thinking: Villains can hire rogue hero to do jobs for them on a contract basis and vice versa. The heroes will then join the villains' team to do a SF. There can only be an equal number of heroes in the team as to the number of villains. It is because conceptually, villains do not want the heroes to dominate the SF; and practically there are more heroes than villains and if the number is not restricted it would drive the villains out of the SF teaming opportunity. That should open the door to more SF/TF experience to both sides and new experience in teaming with a wider pool of ATs.
I know current Hero cannot enter Villain zones and Villain cannot enter Hero's. May be such mixed side teaming perhaps can be organised via Ouroboro: for example, if a Hero is hired to do a Villain's SF, the Hero will be zoning in from and out to the Hero's Ouroboro insteading of the street of the Villain's zones. In that case, the hero might have to sit out one or two missions: mostly those 'Kill/Interrogate some many so and so off the street'. Anyway, it seems doable.
Another venue where this kind of mixed teaming can be organised is in the Midnight Club House, and zoning in and out via a cystral.
The idea sounds good in my head - it does not cost much to develop and it instantly open more teaming opportunities. I wonder what do others think.