This is 100% speculation, but with the very positive word-of-mouth about F&F and its inevitable success once it officially opens, I seriously doubt that will be the last coaster the park ever sees. After years of people complaining about the park being too simulator-heavy and being underwhelmed with how "slow" the rides are, they finally opened a ride that really resonates with people.
I don't think we will see another outdoor high-thrill coaster at the park, but I think their next big ride should be an intermediate-thrill, highly-themed family coaster. Something like Hagrid's. Personally, if they decide to clone Hagrid's for the tram loading area, I will not complain one bit. I don't think they will do that though. I hope to see something of that caliber come to the park, noise and space restrictions aside.
While I wouldn't complain about another dark ride, the park has a fair amount already (And a good line up of them at that!). Now that F&F is open, other than the Supercharged replacement, what I would like to see the park add is (Ideally both) an added live show or a themed intermediate thrill coaster like I mentioned.