Hey Mikerman ! good to hear from you
What are you using .x for?
My current priority is to get seamless debugged and get all the new seamless 3 features ironed out so that anyone will be able to create their own 3d animated movies without bugs and incomplete features tripping them up. So working on different formats has to be a lesser priority for me right now. I have started work on an export for json to help people work with webgl, which is something I have been wanting to do for years, because webgl sounds much more to my liking than vrml or x3d for real time animation but creating animated movies using nurbs is more the thing I am into these days so even work on json is hard for me to justify, however because json is very flexible, it should be relatively easy to modify seamless's vrml export to out json.
I would consider adding .x format if there were lots of seamless users needing it but this seems unlikely while only a small number of people use seamless and .x being one of many different 3d formats out there.