USUM isn't particularly dead, I don't think. Stagnant at the very most, probably, but that's the cycle of literally every Pokemon game ever made. Usually around a few months after release is when hype starts to wane more and more and people start to **** on the games blaming them for not doing enough to give them occupied 24 hours a day 7 days a week. Such is the way things go. Demotivation spreads like a disease; if your friends aren't playing it anymore, why should you? etc etc....
I've been giving this a lot of thought and I get why Gen VII would burn a lot of people out, but it's really no different than getting a burnout from say, Gen V or Gen VI for that matter when both had their periods when people grew sick and tired of playing them over and over again. The most we can do is wait for the Switch Pokemon game to be announced/released and hopefully it'll drive up and generate some excitement that was previously missing with Gen VII.