ie. simply allow the 'shell game' of thaumaturgy-with-evocation's-speed-and-methods to create more varied focused practitioners and specialist wizards/sorcerers?
Yep. I probably wouldn't allow it for starting PCs, but I can definitely see allowing senior wizards to have a specialty field of magic where they are just
that slick. Of course, on second thought I'm not positive that you could be that good at something like magic, which is a function of belief and will, without changing your thinking somewhat (see below).
...THAT'd cause some political turmoil in the Council if it came to light...
Maybe. Then again, maybe not. It could be well known, at least among the higher echelons of practitioners, that attaining a very high level of skill with a given type of magic will color the way you think about everything else. That essentially what I think Kemmlerian Necromancy already does. By learning Kemmler's lessons and internalizing them to the point where a person can put them into practice that person will fundamentally change himself, to the point where his own twisted soul becomes his "sponsor." Yes, the sponsor is not an outside agency, but that doesn't mean there's nothing compelling the Necromancer to ever lower depths of depravity.
Of course, I could be
completely wrong and Old Man Kemmler could be sitting in his grim Netherworld fortress trading power with those who practice his Art, waiting for the day he shatters the borders between life and death and becomes the immortal ruler of the universe.
That works too.