Well, you would normally win the game automatically. Is making winning the old fashioned way that much easier such a bad thing?
Personally I think that making all units the equivalent of Archmages is much too powerful, but I wouldn't mind it granting arcane units the channeling II and III promotions. (I'm not sure if it should just be for new adepts built there, or for those that pass through the city)
(Speaking of Govannon, I would prefer it if he could teach spells of any sphere, but had to know the 3rd level to teach the first one. Of course, that is a change I can do myself easily enough.
What I would really like is if the cave of the ancestors, instead of granting free xp to arcane units bases on the mana possessed, could randomly grant channeling I, channeling II, sorcery, and various first level spell spheres (with chances based on how much mana you own). It would then be really cool if Wizards became just Archmages availible at sorcery (since any unit descended from Kyorlin, even a worker, would have a chance to be born with all the abilities of an other civ's mages), and if Archmages were replaced by a single national unit UU, the Casawallawn, which would be the strongest caster in the game (perhaps starting with hero, spellstaff, magic immune, extension I and II, and perhaps all the spells of all the mana types you posses). Alternately, Casawallawn could be be a promotion that works like patriarch for Amurite arcane units, and grants something like a -100% percent chance of the target resisting the spell.
Also, I would like it if spellstaffs were treated as objects, able to be handed from one arcane unit to another so one caster can focus on making them for the others to use. It would also be nice for it to have some other small effect, like a -5% chance of spells being resisted)