iirc most content available in 3D is Blu-Ray based content. As we do not support direct playback of Blu-Ray discs, it might make more sense to
a) either get a Blu-Ray disc player and control it via LinuxMCE
b) get Blu-Ray playback into a usable state for LinuxMCE
b isn't going to happen anytime soon.
Youtube also supports 3d