I have personally reached the "no more rulebooks" stage with Pathfinder. Unchained will probably be my last. I have enough rules to last a long time. I will still continue buying the APs that look interesting but I do wonder if, between 5e and people feeling like they have enough Pathfinder rules, a downturn is inevitable.
I love a lot of what Paizo does, but I reached the "no more rulebooks" stage right before the mythic ruleset came out. I think the last book I purchased was Ultimate Magic. I don't have any doubt in their business model. I'm sure they have intelligent minds looking at the ins and outs of their accounts. What I do doubt is that there will be a book coming out in the near future, that is not a module or AP that I will even think about purchasing. But I'm only one guy, and there are a LOT of gamers out there who might be gobbling up all the new publications.