We know vampirism is in. Lycantrophy too. We get an extra skill tree for being sick. Both diseases are excluding each other.

Do you think there will be some possibilities besides those two options (skipping both excluded)?

It doesn't make any sense (except for RP) to deny oneself an additional skill tree, but I don't think everybody wants to be some infected gizmo.
I'm thinking of becoming a lesser lich or a lesser deadra. For those who don't like these dark options, how about being blessed by the Eight Devines? (It's easy to find reasons why those options are excluding each other.)
Or something more different: Joining some cult. You will gain their special knowledge (skill tree) and after some ritual or treatment you are immune to vampirism and so on.

Any other suggestions?