When it comes to Swordmages and switching hands with versatile weapons, we are ultimately talking about an increase of Swordmage damage output of 1 point vs the Swordmage swinging the weapon one handed.
Is this overpowered? Not by any stretch of the imagination.
I would imagine the WotC people feel the same way, otherwise why would they have this switching hands thing as a free action in the FAQ?
Of course, DMs can impose additional conditions at their tables regarding this, but the fact remains, we are talking about 1 single freaking point of damage. If it means the difference between a Swordmage player having a fun time at the table, or spending the evening brooding or upset about the DM's ruling, I would let the Swordmage have that extra single point of damage.
P.S. - I realize some people will want to point out the AC difference derived from the Swordmage Warding class feature. If rulings are made to make switching hands a chore or even a nuisance, the player will simply swing his weapon as one handed by default instead, thus making the point moot.
