MP = Mircea Popescu.  Some Bulgarian or Romanian dude who's supposed to be rich.  You might remember his sock puppet thing here who had a female as a picture.  ~mpoe-pr IIRC.  Very caustic style (but usually quite amusing to those of us who appreciate such things.)

The guy is driving an effort to make very cheap nodes capable of running a version of Bitcoin that he likes.  Back in the 5.x timeframe.  The idea is that they could be handed out like candy and Bitcoin would go back to a situation where it was sort of a peer-2-peer solution (one of the mostly BS original sales pitches that is getting quite long-in-the-tooth.)  Frankly I think this is exactly the right direction to go.  If he can make a credible case that he can win a fork war I might even put some money on it since his end-goals and mine seem to align.

So, to answer your question as best I understand, 'mpcoin' would be just an older version of Bitcoin.  If there would be patches and tunings and such expected, I did not run across the suggestion in my skim of things.  I'm not sure where things stood with respect to p2sh and the BDB -> LevelDB switch and stuff at the 5.x version that the MP clan has wood for...and am to lazy to look it up at the moment.  Whether that version accepts and understands all transactions to the 'gavincoin' fork, or just accepts and does not understand them (or doesn't accept them) I do not know.  It would make a difference in some use-cases.