Play as the old characters for a New Game++ type thing. Like once you max out one character, you can start a new game using one of the old Treasure Hunters? It would totally break the story and all but after New Game++ who cares? It would be a great way to reward players for maxing a character. Maybe have special lobbies for veteran players that let you play as you wish. Of course, with all the new guns and features some of the old perks might not work as intended... hmmm,,,
0_0 That would be awesome. I would totally bring Roland to Borderlands 2 if they did. Hell maybe another thing they can do is just transfer your character from BL1 to BL2 as they did for the Mass Effect series.
They would have to massively change them, at the moment, Roland and Brick definately look completely outclassed, and Mordecai is looking barely competitive, however Lillith was already over powered compared to others. We don't have any solid info on Zero yet really.
The original characters are not, under any circumstances, going to be playable. This has been officially said multiple times already.
The reason they aren't playable isn't anything to do with the story. They wanted to revamp the classes, but they didn't want to screw with the actual characters from Borderlands. The original characters are horribly balanced.
Basically, it came down to people would complain if those characters weren't playable, people would complain if those characters weren't exactly the same as Borderlands 1 because anything changing automatically means it sucks, or people would complain if those characters were exactly the same as Borderlands 1 so still completely imbalanced.
The chose the first one as the lesser of all possible evils and based on a lot of other games I've seen in similar situations, that is probably the best option. When the game actually comes out, the people making that complaint generally become a lot less vocal. However, the other scenarios result in people complaining for all time.