Even if he adds 25 lbs., that still puts him at 6-foot, 230lbs. Not exactly NFL tight end measurements. The average tight end weight is around 255-260...I think Swain would have some trouble with his blocking assignments as an NFL tight end. And most of these guys are at least 6-foot-4.
He runs in the 4.6 range...if he adds another 25 lbs., I think that speed will drop off. Most NFL tight ends are running in the 4.7 range...and since Swain would already be undersized at the position, he really couldn't afford to lose a step.
Not to mention, it'd be an entirely new position for him.