We don't believe that Windows RT allows us to add codecs into the OS. A stand-alone playback app would be required. AVI is an antiquated format and we don't intend for AVI + TSCC or AVI +TSC2 to be used as anything beyond an intermediate step between recording and the final production. So even if we do release a stand-alone player for WinRT it would likely be like our SmartPlayer app on iOS that handles h264 mp4.
I'm sorry that this isn't the answer you're looking for, but I'll finish by saying that nothing is out of the question if we receive enough support here for your idea here.