First of I would like to say that I am having a great time leveling in SWTOR so far. I have played with friends mostly and I must say that greatly improves the experience of the game. That being said I wanted to express an addition to the game that I think would be great as well as bring in an entirely new crowd to the game. Story Mode Characters (SMC). Let me explain what I mean.
Currently my highest character is a Sith Warrior. While leveling with friends I did spectate a few bits and pieces of their class story. Then I got to thinking "how could I experience their story myself without running all the planets 8 times?" I came up with the idea that there should be characters that only level from class quests so I could in fact see the entire game in a much more reasonable amount of time. Lets face it, if someone plays one or two characters up to level 50, most people aren't the kind that will sink another month of playtime to level other characters up just to see the story of the class (I know I'm not). This would mainly be because they have already leveled up characters and ground out quest after quest, planet after planet. They have already seen that content and wouldn't necessarily want to see it again. Story Mode Characters (SMC) would completely fix this issue.
There are a few things that would need to be implemented to get the framework into place for this to work:
1) SMC would only be eligible for class quests. This means NO FLASHPOINTS, NO PLANETS, NO HEROICS, NO PVP, NO OPERATIONS, NO GTN, NO CRAFTING. These characters are only created to experience the story of the class, not so people can get a Sith Assassin to 50 for next weeks raid.
2) EXP rewards would keep you at the correct level for all your class content. You wouldn't need to worry about not being high enough or out leveling class content. Often times this would make content more of a challenge and appeal to a crowd that likes a boss fight to be tough.
3) Loot rewards would need to be overhauled for these characters as well. Not only for the players but the companions too.
These are the basics that I have thought up on my own. Feel free to add suggestions to this list. This feature I think would attract a whole new player base to the game, as well as coincide with Bioware's innovative look at a genre that has gotten stale over the years.
TLDR; Single Player Story MMO