I'm not sure it would be a good idea for Obsidian to make it "officially shown" that Revan and Bastila are an "item".
A lot of people disliked Bastila and didn't want the romance angle. So forcing a romance on them would probably bring about some angry KOTOR2 fans.
I think if both Revan and Bastila are appearing in TSL, it'd be best if their relationship is "ambiguous". For instance, if they appear together, Obsidian should probably exploit the "master-apprentice" relationship as the reason they're together, instead of a romantic one. That way, those who want them to be romantically involved are happy since they're together, and those who don't want a romance are also happy.