I really have not roleplayed in MMOs up to this point, but with SW:TOR it seems conducive to do so. The game itself is said to be story-driven so people will become in touch with their character. Also, the Star Wars lore is not a hard thing to pick up so many people will be looking to roleplay I believe (or hope).
The backstory of the guild, as I have sketched out so far, is that it will be a smaller sect within the Sith Empire. The members of this sect are direct descendants of the original Jedi who were outcast after the Hundred-Year Darkness. If you wish to join the guild and roleplay this out I would ask that you don't pick characters already documented and in lore, it seems open enough to where you could create your own ancestor who was an original exile.
Anyway, I envisioned the sect to be something like "Descendants of the Fallen Empire" but after so long they simply reduced it to Fallen Empire as blood thinned over the centuries. I am not, in any way, placing constraints on how anyone wishes to roleplay this. You could play a character still bitterly angry and boiling over with hatred toward the Republic and Jedi in particular who had your forbears outcast. Or you could go another way and have a Sith that was indoctrinated in these ways but holds regret over what happened so long in the past. Heck, you could even roleplay someone who isn't a descendant of an exile and simply gained the respect of those within the sect and was asked to add their strength.
My point is simply this, this is the backstory I've dreamed up for the guild but there are no restrictions. Roleplay how you wish, if you wish, and have fun. Some source material for anyone who wishes to take a look at it can be found at the two links at the bottom of the post.
Fallen Empire will be a guild that is a bit of a jack of all trades. I envision it to be a very social guild where people come to gather and play and enjoy good company while they do so. I envision it as a roleplay and PvP guild as well. The two going almost hand in hand with how the galaxy is in turmoil and on the brink of all-out war. There will be, as I said, a position such as Roleplay Officer or Council or somesuch that will put together roleplay events for the guild. These events and roleplay itself will not be mandatory but they will be encouraged.
The guild will be started on a PvP server (Bioware willing) just for the purpose of having as much 'realism' as possible to the war between the two factions.
More will be added as it is thought of, or as others bring questions.