I definitely think they should have the Sages battle. Yes throwing in Peons is great, but why have unique characters if the extent of their use in the game is to get captured and mock your character, gym leaders, and so on. Rocket, Aqua, Magma, Team Galactic had their Admins excluding Charon. So I don't see why they can't expand that into Plasma. This can give you something worth while to look forward too post game. Heck they don't even have to limit their teams to Unova pokemon at that point, giving them more of a diversity of what to choose.