I'm that guy working on native support for bluray in mplayer. A patch has already been submitted. It works (for AACS only) - just pull it off the net if you want to try it out. But it's v early days so expect issues.
We're currently discussing if there are better ways to go about the whole bluray (aacs/bd+) thing and there is something in the works by some other people so stay tuned...
