I'm assuming it will be like before, where you can join all the guilds if you wanted.
I don't think choosing Imperials or Stormcloaks will have a major effect on what guilds you can join, that would just be taking customization and replayability out of the game.
ok cool, i thought it would be cool if you were bound to one and became rivals with the other guilds or something liek that.. for example, if you want to join the mages guild you would need high lvl's in magic spells in order to be eligible, thieves sneak, and etc. etc. making so you would need another play through to experience the other guilds... but i guess its for the best anyways