A slight change to SR:

Super reflexes is an odd defensive set. It is more easily able to soft-cap than any other set, but gains little other benefits at the high end. Shield, the closest direct comparison, gains huge amount of offense and can get to higher levels of survivability through higher constant resists and +HP and having a larger selection of mez immunities.

Here's my proposal to fix this in a way that isn't overbalanced and doesn't transform SR into SD #2. Add a fairly large damage and +hp buff to one of the toggles, or spread it through the 3 of them. I'm thinking about 50% to damage and 10% buff to +tohit. However, that buff would go down as more enemies are within range, to 25% to damage and 0% +tohit. However, as more enemies surround you, your +MaxHp goes up, up to 10% (so, for 5 enemies, you would have abobut 37.5% to damage, 5% +tohit, 5% +MaxHp). Stalkers would probably have a constant buff equal to 5 enemies in range for other sets.

The rationale behind this change is that your reflexes are good enough that you can spot the weaknesses in your opponents defense at lightning speed, giving you an offensive boost. However, when you are surrounded by enemies, you would be unable to use that advantage because your focus would be softening the blows of your enemies, dulling the pain. The +MaxHP could also be a +resistance buff if that would work better.

This would change SR by giving it some offense while still making it separate from SD. The "reverse AAO"-affect would make an SR scrapper have an advantage against single targets on offense, and be slightly more defensive against large numbers of targets, and would add an interesting amount of strategy for the SR scrapper.

Any thoughts?

It's certainly an interesting idea, but what about the other AT's?
You mention Scrappers in your post, but IIRC Scrapper SR was never changed to generate agro the way Brute and Tanker SR were. This leads me to believe that Scrapper SR is not intended to be drawing excess agro. As this change is based on agro it may not be appropriate to apply to Scrappers

For Brute and Tanker this makes plenty of sense since they already have a taunt aura added to Evasion.

Also what would you do for the Stalker version?

I find Super-Reflexes is pretty much fine as-is. Yes, it's not as versatile as Shield Defense, and Shield Defense can potentially out-defend it, but Super Reflexes is also much higher at its baseline, requires considerably less sacrifice for the sake of soft capping it, and better resists Defense debuffs, allowing it to remain soft-capped even against problem enemies.

SR may have a slightly better baseline, but I still believe that sets should be balanced at both the base and the higher end. I should be able to make an argument for SR against SD (and vice versa) at every level of investment. Currently, SD is simply better in every way on all but SOed or basic IOed characters, as it gets equal defense, equal DDR (with HOs), better resists, better MaxHP, a useful god-mode, more team utility, and of course, more damage. This would simply even the floor a little bit in a simple adjustment.

And for other ATs, here's what I would do:

1. Stalkers would get a passive damage bonus of about 37.5%, a tohit buff of 5%, and a max hp buff of 5%.

2. Scrappers would get the same power as brutes and tankers, but have it set not to aggro, as well as to have a slightly higher damage buff (as per AT mods). This wouldn't be gamebreaking, as the power would do nothing against enemies, unlike other auras that have a debuff associated with them. Of course, we could also give stalkers the same version as scrappers, but they are supposed to be more self-contained.