Oh, definitely--good point~ Solo mode would be intended to be like the solo questing, so with a companion of your choice. Which, now that you mention it, isn't quite solo
In further goodness of you point, having a "solo-able" continuous end-game zone with a leaderboard is contingent on the idea that various combinations of player classes and companions are pretty balanced. If one class has an OP companion, it might throw things off a bit--but that'd be a great way for Bioware to get some handy player-spaded comparative data! And another reason why leaderboards would be per season XD
Good observation~ I'm glad you like the premise!