He's not the first youtuber to completely abandon being on camera. Granted, most times I've seen it happen it was smaller channels with like 100k subs. But they simply stopped uploading and never came back. At least mat told us he was leaving.
In the last meme review he did say he'd like to do something like taskmaster, and he did campaign hard to host jeopardy. So maybe he plans on trying to become a gameshow host. But like i said, he only wants to be the talent, and not have to do all the behind the scenes work as well