I think that he's a pretty good athlete, but he would need to be an amazing athlete to make that transition. It's hard to make up for time lost playing those positions, so the chances of him being ready to do so at the NFL level with no college football experience at that position are very slim. It requires a very different skillset as well as mindset to play defensively. Assuming that he has the mindset, which is a big leap, we don't know if he is able to do things like pick up the ball in traffic and react properly or dish out/take the punishment physically. Even if he is able to do these types of things in a vacuum individually, putting it all together with no college experience and being a successful defensive player at the NFL level would be difficult.
He's got a decent head on his shoulders and he works hard which I admire and I don't like to count a guy like that out, but I think that it's a very tall order. I'd like to see him do it, but I would bet against him doing it partly because I still think that he would be more successful offensively.