I'm definitely against disarm in 4e. With one action against a Swordmage you could simultaneously remove his implement, his weapon, and drop his AC by 3. THAT isn't over powered?
Secondly, disarming in a climactic battle sounds like a perfect opportunity for a skill challenge.
With a minor action he can pick his sword back up. So, no.
You need at least two standard actions - a disarm and something to move him, and then a minor action to grab the weapon. Not all monsters have a (good) forced movement power; those that do might as well put it to use.
Compare the disarmed swordmage against two normal successful attacks. With two actions, a Swordmage could lose half his hit points / be prone and dazed / stunned and damaged / etc. Is it still overpowered considering that?
Maybe.
That is an interesting idea. I wonder how it would work out?
First off, the trip and disarm maneuvers are represented in the game through powers. This is a major mechanic baked into 4e. Many powers knock an opponent prone. Disarm is the sole providence of the Fighter but other characters can easily get the ability through multiclassing if it is essential to their concept.
To start with the basics, I don't buy into a combat maneuver being defined as "usable only by a specific character class once per encounter or less or someone who has spent two feats to cherry pick this same ability.