OT is a framework that actually has nothing to do with phonology specifically.
Here's an example:
http://languagelog.ldc.upenn.edu/nll/?p=1129In that sense, OT hasn't changed in the last 20 years. On the other hand, the specific constraints that are implemented and whether they are universal or language specific is an issue of debate and different proposals suggest different details.
OT isn't my area, but I think this may be more along the lines of what sieledorothy is asking about.
More specific questions:
"Which constraints should I include?"
"Which constraints best account for what?"
"Where do these constraints come from?"
So in this sense, OT isn't so much a theory but a family of theories. I'm not sure it's even falsifiable, given that you can just try out different constraints infinitely. (You might find some way to suggest that, in general, constraints aren't violable, for example, but I'm not sure how exactly you could do that.)