After spending some time exploring different functional languages, if FP does make it at all - my money would be on Haskell. There is something to be said for focused languages that does one thing but does it really well, and the feeling of security when a certain style is enforced over a codebase.
I probably wouldn't use it for anything today, but in another couple years maybe. The ecosystem seems like it's reaching critical mass.
I think Clojure is ready right now. For "standalone" languages haskell seams to be on a good way, some people are allready doing start ups with it.
Actually most Lisps offer optional means of static verification and static typing for when its necessary. Furthermore, Lisps have vital metaprogramming features that Haskell lacks which are essential for symbolic AI applications.
So, why didn't Haskell become more popular earlier? I think that's simple: the GHC compilers has improved tremendously over the past years, Hackage has grown considerably, and there are now more books oriented at practical programming.