The upside is, everyone I've talked to who plays a Shadow really enjoys it at endgame. So, I suppose you can try pvp leveling and just wait until the last possible moment to finish class stories. I deleted my JC at lvl 14 to make room, and don't regret it. Enjoying the Trooper story so far.
That's basically what's keeping me playing my shadow. It an extremely fun class to play. I got to Quesh and i can already see that it's gonna be the same old same old. Oh well, at least the Sith Inquisitor story seems to be pretty interesting in Ch.1