If anyone is bored or really wants a challenge. This was a suggestion I had a couple years ago:
The basic idea is to use multi-threading to make MKV playback better when streaming to the PS3 (i.e. on the main thread play MKV on the fly like now, but on a background thread remux the MKV to a M2TS (cache) - when the remux is complete - switch over to the cached source instead of remuxing on the fly - at this point rwd and ffwd would work (unlike with on the fly MKV playback). The huge challenge would be the switch over of playback. I don't know if you can ignore ffwd and rwd requests until the playback has switched over to being from the cache, but that would improve the experience.
PMS already does amazing things, but MKV is the most common format for archived HD content, yet anyone who has ever hit the RWD or FFWD button when playing it via PMS on the PS3 knows how crappy the experience is.