Looking at the patch notes that have been published, it certainly looks like Spellslinger has lots of healing abilities, and like Stalker has a lot of tanking abilities (although it's possible they're not as effective as intended). It also seems like Carbine is fairly focused on balance, since they already changed Warrior threat generation to be the same as Stalker. Of course, balance can never quite be perfected, but I think the biggest disparity in which classes we see will doing which roles will be a result of the player-base's affinities. Many people who like tanking will naturally just choose Warrior, where as most people who choose Stalkers will probably want to be DPS assassins. In WoW I remember there was a point where Druid tanks were stronger than Warriors, but they were still fairly rare. Once a class becomes overpowered in a role they do become plentiful (*cough* paladins) but I get the impression that Carbine is going to do their best to avoid that.