I'm inclined to say that we should keep class mechanics out of the political factions, and have them just be about their different points of view.
It kinda annoyed me that Morrowind felt the need to stick the whole combat-magic-stealth thing into places like the Great Houses and the Vampire Clans. It felt forced.
While that's a good point, I think that there's something to be said for giving each political faction its own mechanical identity, as well as its own flavor. It helps reinforce what each faction is about, and makes them more distinct from each other.
- Nord traditionalists are of course going to be all about fighting up close and personal. Ranged weapons and magic are dishonorable.
- Any faction based out of Winterhold is going to have access to plenty of magical resources (the Ysmir Collective and the College of Winterhold, primarily) so they'll naturally draw on that advantage.
- The Empire has a powerful military, but it's just as reliant on spies like the Blades, and is much more concerned about diplomacy and legitimacy than the Nords would be. And, of course, an emphasis on stealth and diplomacy underlies exactly the sort of Imperial deviousness the Nords are rebelling against.
Hunters' and Traders' Guilds would be cool, too.