I'm totally for OGG, over MP3, and i'd happily welcome support for OGG renders on BotB, except this creates a problem as to what to do with already existing entries and if we should allow both formats or just one for all the future ones. Converting everything that's already there is an awful idea (reencoding lossy to lossy? Yuck), so i'd just keep it untouched, and enforce OGG for all new uploads.
Or like Razero said, give people the choice to upload either Vorbis or Em Pee 3, just not both for each entry
Also i don't think it requires any external support for major browsers, for example Firefox and friends were capable of playing OGGs served directly for ages already