[Tyhm]

Anoo, the two are quite different. A short sword isn't just an abbreviated version of the diamond sword. A full sword is heavier. It takes more strength to swing, your strategies must take into account how long it's going to take to connect and how vulnerable you'll be afterwards. Likewise if you swing a knife as slowly and awkwardly as you swing a sword you're not going to get very far.
I could picture a mage who can wield a dagger but is too weak to usefully use a sword, and a knight who's useless in a knife fight. However, I believe that the inability to PROPERLY wield a weapon shouldn't bar a player from IMPROPERLY wielding one. If a wizard wants to hold a sword, fine. Anyone can HOLD one. Then as they stand there they wobble and slowly pitch forward...they swing it slowly and hit themselves in the leg half the time...maybe they occasionally drop their weapon/lose their grip entirely...

If such a change took place, everyone currently with melee should have both skills, I think.