We are all getting older. More and more people leave the game year by year because Dota is a very time demanding game if you want to be good at it. Valve also fails to solve the smurfing, boosting and account buying problems the game is plagued with for more than half a decade now. Nor the anime neither a new player experience update will very likely bring in new players.
A MMO would be too big for Valve. It would probably need more employees than Valve has overall. But an ARPG sounds realistic. Event modes like Siltbreaker were really fun so Valve definitely knows how to make RPG Games.
I'm reaching an age where i prefer not to spent so much time into Dota, also because it can be really stressful at times which affects my every day life at uni and work. But i also don't want to abandon the Dota Universe and would love to play something casual. Something like PoE, just in the Dota Universe sounds like a really fun thing and i hope that the old Underlords and Artifacts devs are joining forces with some Dota 2 devs to create a new game.