make mind spike our alternate nuke by not removing dots.
In fights like Will of the Emperor where the adds die to fast for your dots cant finish there damage. it would be nice if mind spike had like 5% more damage and didn't remove dots so you can put your dots up and and spam mind spike with out worrying about your dots removing that would make fights like that so much better.
Yeah they had that in the beta of cata and dps was insane. If you can do it on adds that die fast you can do it on the boss. Mind spike is supposed to be used when you are on adds that won't live long enough for your dots to be useful, you just want both and that would pretty much double your dps (+5% even on top of that as you suggested) That would be a broken system and would never happen.
I can't really see any situations where it wouldn't (depending on the tuning) either replace mindflay or still never be used in pve scenarios (outside of flcd), I'd rather see other buffs than making it another mindflay.
I think this would make shadow priests quite overpowered for those situations. We might not be the best class for single target or multi target fights even, we are far from even currently. But the good thing about those adds is that u can just DoT them, which might not do amazing damage, and switch to targets with a higher priority like courages or strengths on fights like will of the emperor and it does give a lot of procs on ToF which is very nice.