My 2ct,may not be much worth, but I'll go ahead anyway:
Why spend the time wasting cycles encoding MPEG2 data, only to decode it in the video processor?
Couldn't 'your' effort (or the researcher's effort) not better be spent optimizing a decoder for the Pi's hardware?
The CPU is more than enough! Even on an x86 processor,you only need a 300Mhz processor to decode mpeg2 data, dvd quality.
The issue with bandwidth is also questionable, as loading the video and audio stream uses only a fraction of a USB2 interface's bandwidth.
Thiking that most mpeg2 data would be of DVD quality or lower, not HD quality like of blueray dvd's; and should be playing back on an RPI (correct me if I'm wrong, and if I'm wrong then there's probably a software bug preventing it from happening).
Otherwise,playing back HD mpeg2 could indeed reach the limits of an Rpi! I know that if it's capable of decoding 720p mp4 (avc or h264) video's, that it's quite an accomplishment, as the x86 architecture needs an 800MHz P3 the least to do that job!