TL:DR: Most former Ensemble Studios developers have moved on with their lives, and no such thing will happen.
That will never happen, the main reason being that Ensemble have moved on from Microsoft and Age of Empires completely. This is a key reason why Robot Entertainment, the main successor group of Ensemble only make weird, oddly specific genres that are only really popular among Chinese and Korean gamers.
As for why they don’t like Microsoft: It’s because of Microsoft Ensemble no longer exists as a unified entity, it’s because of Microsoft Age of Empires is a dead horse kept alive solely by people wanting their nostalgia fix, or alternatively the ESports community upholding the games because they are garbage at StarCraft 2. It specifically doesn’t help Microsoft shut down Ensemble, and then made Relic Entertainment work on Age of Empires Online shortly afterwards, just for Microsoft to pull the plug, tell them to rack off, and grant the game to an unknown game developer (that IIRC, doesn’t exist either anymore) because it was more convenient and cheaper for Microsoft; we know how that turned out.
There have been a few exceptions, but those few were either low on the Ensemble totem pole, were fired, left , or were involved in the series later on during the Microsoft era. Matt Prichard from memory was only involved on the second game, and Rise of Rome from memory.
Finally, the only person actually willing to talk about their time in Ensemble is Sandy Petersen, but even then when people were interviewing him, they were only asking about AoE2, and his general reaction to many of those questions within that livestream showed that he was getting mad, holding his tongue, and telling lies not to break NDAs and such. A big point implied by him? He didn’t like where the series is going, and he doesn’t like Forgotten Empires either. So he will definitely not return.
From my experience, the rest of the devs don’t care about AoE or AoM anymore. Especially the lead designer of Age of Mythology; Ian Fischer. Me and a friend of mine (who was indirectly responsible for Bruce Shelley giving some development stuff, builds, etc to a game pre-release archive museum, and also asking Tony Goodman a similar question, which resulted in the AoE2 Design Document and other builds of pre-release material being made public) were asking about possible archived AoM media and such, all we got was either static, or deflection, so we decided to give up. So obviously he has moved on with his life, and wants nothing to do with the series anymore.
Hell, I even emailed Kevin McMullan (who directed or made the music for AoE1 to Halo Wars?) about an interview for AoMH, and once again; got boo. This was after those two videos of him replaying AoM music by the way.