So, there's clearly space for another attraction if they wanted it (e.g. where they put the parking area backstage) in Pandora. I wonder whether they would ever consider adding another attraction to the land. It's hard for me to see a situation where they say "we want to invest more money in Pandora" as opposed to building an attraction elsewhere; but at the same time, they did seem to allow for space to provide that option.
The bike coaster idea though seemed to be similar in concept (though not execution) to FoP, I thought -- the premise being that it was you riding on a banshee around the land. Would seem to be redundant if that is the idea so I don't think we would see that added; furthermore, a coaster like that would probably have it's best impact being built at the time of the land so it could weave among the detailed scenery. I feel like it would be hard to effectively add it later without shutting down the land or just ignoring the rest of the land and putting everything in a show building which would miss out on the most compelling aspect IMHO. Even if the concept of a coaster wouldn't be riding a banshee (maybe it would just be a helicopter tour or something), it would probably be ideal if it was build with the rest of the land.
That all being said, I think the land and DAK would probably benefit more from an additional dark ride than a coaster, if they were to add something. Pandora in general seems like something where show and effects are what would set it apart, more than thrills.