We don't know much about this game, but I can definitely see it being a good series as long as they don't lose their vision. Having said that, Mikami DID say that getting the horror right in this game is pretty hard, and that it's hard to scare players these days because they become accustomed to the scare tactics people use in games and movies. It could be pretty difficult to come up with new things that continue to scare people for three games in a row.
Even if The Evil Within was just a successful one-off game, it would all be worth it if game developers saw it and were inspired to create more survival horror games because they're enjoyed and are profitable. The big developer I have in mind is Capcom, which I'm sure you all knew that lol