It is
highly unlikely, for many reasons, that there will ever be Musepack support in iTunes. Not to speculate, but there has been at least some level of testing with FLAC in OS X Leopard, so perhaps there's a remote chance that we might see native FLAC and Ogg support in applications like iTunes. FLAC support would be a definite boon for Apple, since loads of users (myself included) choose FLAC as their preferred archival format, and since it's so inconvenient to convert FLAC to Apple's only good lossy format (AAC), there are still lots of hold-outs who won't use iTunes as their default audio player.
I have an new iPod, so for the sake of convenience, I just batch convert my FLACs to LAME with foobar2000 and add them to my iTunes library. I won't switch from FLAC to Apple Lossless, however, so for home listening via my hi-fi system, I never use iTunes as I can play my FLACs with foobar2000. And of course my trusty Karma is still going strong with 20GB of excellent-sounding yet tiny Vorbis files 🙂