If you run this, what would the mechanics be like - a lot of them, very few or somewhere in between?
This is what I've been trying to wrap my head around all day. I don't want straight-up strategy as the personal level of the players should be important here, but going too personal might leave everyone having their own private adventures and cause problems with time.
The magic system needs adaptation, as it was more meant for a smaller-scale RPG. With the power level of the players they should really have an endless list of spells to use and a vast power reserve to use. As you can probably imagine, this is not the ideal thing to implement. On the other hand, just generic magic rolls for everything is pretty dull. A compromise could be giving the players a handful of useable powers according to how they describe their style of magic, and handling 'lesser' spells with generic rolls. But I don't think this is good either. I might just go for simple rolls, making it not-dull with the power of Narrative (and/or the players' own RP).
The difference
*Archmage A crafts together a
Strangler Hex [Body 3, Primal 1] against the usurper. The poor man fails to counter the spell and goes down with invisible ropes wrapping themselves around his neck and body. [Damage: something something] [Probably some other mechanics here, too]
*Archmage A magics at the irritating usurper. (Magic Roll: 4) vs (Magic Roll: 4) He strikes fast, lashing out with eldritch lightning, but his opponent deflects it at the last moment with a shimmering ward. The two men begin crafting the Art at incredible speed, cascading waves of magic rolling against eachother between the duelists. They are evenly matched - when the Archmage calls down lightning, the usurper deflects it and follows up with a spectral lion of fire that nearly slams into the Archmage, but the older man disperses it with a snarl and a thrust of his staff. And so on and so on.
In any case, as the focus of the game is on politics/intrigue, though also magical discovery and investigation, combat need not play such a big role - so I think the latter approach might work better. Non-magic combat would work much the same, though just going with 1d6 vs 1d6 a bit oversimplistic, so I'd likely improved it somehow. Especially when modifiers come to play.
Social actions, like persuading someone, I'd generally fully do with RP rather than rolls. Always more fun that way. Most actions would be simple rolls, maybe with a Difficulty rating to beat. This generally works well enough.
Advice/criticism is welcome - I wouldn't have written any of the above otherwise.