i had a similar idea with the spine/elec scrapper i made whenever they proliferated elec armor to scrappers
heres the build my guy is currently using, its not much different than yours but prolly a tad cheaper cause i dont use pvp IOs at all
Code:
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I run a Spines/Dark/Blaze who has all of 1 "melee" attack in his chain. If you can call Ripper a melee attack.
Fire Blast, Ripper, Throw Spines are really all you need at decent recharge - especially if you are using Spine Burst and Fireball as well. Current in game build doesn't have Impale (I know, sacrilige, but since I can blast almost twice in the time of an impale cycle ...) and Lunge is just there to hold a KC. 
2 dmg auras are the bomb. As /elec you would have less endurance problems than other spines/XX/"not body mastery" builds.
I will say it seems counter intuitive, but a ranged scrapper is fun as hell and has no trouble with those inevitable broken will runners. Do it, it's awesome fun.
Thanks for posting this. Been toying around with the idea some time ago, with a claws/regen/body that'd be full ranged, but the redraw made me want not to do this.
Now we have KM and Fire epic... Hmm.
Focused Burst -> Fire Blast -> Fireball -> Focused Burst -> Fire Blast -> Ring of Fire could be a gapless attack chain. Might just do that on a second build.
I wanted to see, just for kicks, what a ranged scrapper would look like. The build I came up with has something close to a ranged attack chain (throw spines > impale > shuriken, with exploding shuriken tossed in whenever possible), two auras (which I probably overslotted) that keep guys out of melee, and some nice perks like perma hasten, but goes solely for resistance for protection instead of something better like soft-capping ranged defense. Of course, this guy is supposed to be part blaster, so you don't want to go crazy with survivability, but a little is nice to have ;) This build also has unneccesary recharge and probably needs more endurance, so there's lots of room for improvement.
If you think different powersets would make a better scraster then go for it, but spines seems like the obvious winner for primary. I chose elec because of its damage aura (do two damage auras scare guys away twice as fast? Or does quills make the second one unnecessary?) and recharge boost but I didn't really try the others so maybe they're better.