I thought the Engineer-specific interrupt was because Engineer was the "least-popular" class chosen overal, so it was a way to show them a little love.
Still, I think the idea of class-specific interrupts is a terrific idea, but care needs to be taken that it doesn't railroad a player into choosing a particular class.
In other words, don't have a Vanguard-specific interrupt that actually punishes a Sentinel. Have the class-interrupts provide a small bonus WITHOUT inflicting a penalty on an "unoptimized" class selection.
I.E.
a "mexican-standoff" scenario between Pirate Leader and You, your squadmate is held hostage.
Vanguards can CHARGE into the Pirate Leader (Paragon) or CHARGE into the munitions crate behind him (Renegade) thus freeing your squadmate.
Charging into the Pirate Leader takes him out and minimizes collateral damage, but puts you in direct fire from the Pirate Leaders' minions.
Charging into the munitions crate takes out some of the minions and the Pirate Leader, but harms your squadmate.
Other classes would simply have the "regular" interrupt to either shoot the Pirate Leader's weapon, causing it to jam (Paragon), thus giving your squadmate the split-second needed to break free; or to shoot the Pirate Leader, but leaving your squadmate to take a hit from the minions as they break free (Renegade).
Essentially the same scenario, but with a different flavor based on what your character can do class-wise.
It's not a perfect example, but I'm sure you guys get what I mean.
It doesn't have to be ultra-ground-breaking-awesomesauce, (since that would inflict the aforementioned railroading) but something on a smaller scale that doesn't penalize you just because you don't specialize in an omnitool or sniper rifles or some such would fit very nicely in Mass Effect gameplay mechanics.