I'm gonna be honest, I'm really, really hoping Gen 9 isn't next. Not because I want a Sinnoh remake (well, I do, but that's not the main reason), but because I don't think Game Freak learned from what went wrong with Sword/Shield.
While Sword/Shield's DLC does show that Game Freak understands the primary complaints about Gen 8 (removing Pokemon, being visually unspectacular, being overly linear and handholdy), Sword/Shield was the product of a dev team that's already too small to complete Triple-A game being split between multiple projects at a time. There's absolutely no way they developed a fully realized and completed a $60 experience that would live to everyone's expectations with a 100-man development team in 2 years, let alone a team of that size fractured between a new entry and DLC for the previous game.