I too would like a longer playlist. I tried it on my BDP-1 earlier and tried to play around with different firmware versions and could not get it to change from 300.
I usually put an album at a time in the playlist at a time. 95% of the time not more than 50 songs. However, I do have a few compilation playlists of 600 and 800+. If I try to load it in the BDP-1, it only loads the first 300 in a row. I have no option to further add. Secondly, if I wanted to add tracks #301-600 on the playlist, it'd have to be done manually by clicking each track. It'd be good to be able to just hit the shuffle button and then just click on a playlist and let it play...However, I suppose MPD isn't built that way?
The other option would be to split those playlists into folder chunks of 300.