Narnia True20 got my juices flowing, and then I suddenly thought of Nisarg's Immortal Rome game.
In a blinding flash, I thought of Amber True20! True, it's hard to beat the diceless RPG, but True20 could work very well.
Basically, virtually everyone vaguely humanlike out of Shadow would be at most level 4, for legendary individuals. Your average Amberite or Chaosian would be, say, level 3. Your typical royal would be, oh, level 6-10. Benedict would be something like 12-15. Oberon or Dworkin... don't ask. :) PC's, if playing the typical "kid of a royal" game, would start at something like 4-6.
Give considerably more points for stats - something like 10, and raise the caps. Add in a few rules for accelerated healing. I'm not sure that one really needs backgrounds, but you could if you wanted.
The basic powers would be feat chains. Ye Basic Pattern would let you shadowwalk. (Easy enough to adjudicate on the fly, as I can say from experience with the DRPG.) Further feats would be things like, "Find Object", "Alter Reality", etc. etc. Some feats could be General (though requiring a certain bloodline), others could be Supernatural, to require dipping into Adept, which is very appropriate. (Making trumps is Supernatural, for example. But Caine's trick of Trump Spying needn't be.)
Keep the Adept role, trim the power list to taste. (Dominate doesn't seem very canon to me, for example. They'd have used it in the books if they could!) Trumps are plot devices with specifically defined abilities.
This is just a very rough first sketch, but what do people think? Is this worth pursuing? Got any ideas?