vvv has stated that the BD output for mobi is several versions behind the current mobi level. It is one of the items on his enhancement list which itself has no publicly released milestone dates -- it may be released this week, it may be released in a year or more.
When we first released mobi books (with the PRC extension) there were only a few takers as the iLiad had just acquired the ability to read them. With the release of the Gen3 and now the Kindle the number of downloads for mobi books has grown. For most books the number of downloads for mobi is still below that of Sony but the gap is closing and for a few the mobi is format is more popular than the Sony.