Would Beth really allow a character that has wielded a single one-handed weapon all their life to effortlessly shift into dual-wield? Seeing how they've split combat skills acording to wield style, Dual-Wield is the most logical candidate for the sixth combat skill since it is, essentially, a different approach to combat.
With that, the list of combat skills is One-Handed, Two-Handed, Dual-Wield, Block, Armor and Smithing.
Thoughts?