Looks like an interesting variant, and a nice looking map. I enjoyed reading through your playtest summaries, as a variant designer and playtester myself. I'm all for people posting in the BGG Diplomacy forum, since the Diplomacy community seems pretty splintered. It's probably just one more splinter, but at least an easy-to-find splinter...
Have you found in playtesting that the random Detached Power allocation matters to balance? Or does the theatre split even it out?
The question of "balance" (in regard to the detached powers) is a tricky one, since I don't have quite enough data to speak intelligently about it.
I know there are some balance issues with France at the moment, but that's independent of the power combinations.
What the detached combinations do provide is a pretty stark difference in player interaction. Certain pairings, like Denmark-Norway with Shawnee, can partially isolate British Diplomatic efforts by reducing the number of players immediately nearby.
My players so far, especially the repeat playtesters, have seemed to enjoy the differences from game-to-game. The ongoing playtest includes a Denmark-Norway pairing with New Spain, and that player has been growing a substantial naval force on both sides of the Atlantic.