Matt is a small ball guy and not the type you want to keep throwing out as an everyday centerfielder. I have no problems having his speed and defense as a late inning replacement or stopgap service for injury. Even if he picks up the weight, you are scarificing his tools now for an un-realisitic tick in the bat. He is a slap hitter and there is nothing wrong with it, but his bat speed and pitch reconginition will likely not improve enough to give him a level of everyday type.
Plus he has a maxed frame and age suggest that what you see is what you get.
If anything, he needs to work on communication and leadership skills this winter to get a bit more vocal in the field. He has to work on situational hitting a bit more, learning to do all of the small things that make him a useful 24th or 25th man on the roster. Not everyone is destined to be an everyday guy, but his skill sets can lead him to a productive role player and still something to hang his hat on with the Orioles. There is no shame in role players.