I'm told he can't learn 2B because he's left handed and evidently that's akin to the plague at the position.
A lefty 2B would have to turn all the way around on any ball up the middle to throw after fielding, making him pretty much useless in that direction. So he'd have to play waaaaaay up the middle, leaving a huge hole and resulting in most plays being to the backhand. You wanna watch a dude who's never played infield try to make that play? I would - just not with the Nats. The over/under is probably 100 errors (seriously).
And how would a lefty 2B turn a 6-4-3? You'd have to either to a full spin while transferring the ball or turn your lead leg through the path of the sliding runner while catching the throw and chucking across your body. Even if we weren't discussing a dude with a janky ankle and knee, that's a disaster waiting to happen. There really are good reasons lefty throwers don't play 2B, SS, and 3B - any ball to the fielder's right is awful to throw.
Also, um, teaching outfielders to field ground balls at the age of 29 or something isn't an easy thing. It's much easier to go from playing infield to playing outfield than vice versa, even if you throw righthanded.