Im firmly in the camp that feels Jaws or BTTF will never happen again, but I dont think its as unlikely as some feel it is. Jaws I would say is the least unlikely of the two to have its own full attraction mainly because, as others have said, the Jaws we used to have was pretty much the perfect Jaws ride. Its an IP that to do it justice would use a lot of land and im not sure it has the nostalgic feeling that say BTTF, ET or the Monsters have. The main arguments against BTTF is the whole 2015 thing and that Universal arent interested in older IPs, both are big negatives but I dont think they are the nails in the coffin that some might think.
We see all the time in attractions that back stories are created to seperate the attraction from the movie or IP, Avatars FOP is a perfect example of this where an entire story is created to do this and just uses familiarity or moments/characters to create an excellent attraction. To me, what gives BTTF a chance is the Delorean. Its the most memorable item from the movies and its a god damn time machine. You can create an attraction from that without needing anything else from the IP. The 2015 factor is easily negated by the fact that only one of the 3 films ever took you to 2015 anyway and you could base an attraction around either 1985, 1955, 1885 or even a new future if you really wanted to loosely base the attraction on timelines from the movies.
On Universal not using older IPs, fine, but nostalgia does sell. Granted Disneys animated classics arent exactly a direct comparison but if they can base E-Tickets on 80 year old movies, then nothing should be overlooked. Particularly when Universal isnt exactly rich in IPs that are adaptable to theme park attractions, especially when they have a hell of a lot of new land to fill over the next 10 to 15 years.
Conclusion: Yeah its not happening and im just playing devils advocate, but maybe its not really that unlikely.