Something similar was proposed before, but it's not quite what I have in mind.
Consider a character that has bought all possible skills. How about creating a further skill list, but from which the player could pick only a single one? Once he does, the others would be unavailable until his death. That skill would give a certain bonus, a crafting option, or special combat move. It could even allow poison crafting or alter the player's speed or inventory space. It would be more of a perk than a proper skill, although for simplicity it'd use the same interface.
In my opinion that would encourage specialization and variety of playstyles. Combat would be fun too, since you would never know which perk the opponent chose. Village jobs would be interesting to manage too.
Since alts are expected to be harder to come by in w8 I believe this would be a feasible feature now. FFS, characters would have meaning.