First, Swain is a senior, so...
I think Meachem has definitely played his way into the upper group of WR prospects, but I don't think he'll leave. I think it's questionable whether or not he'd go in the 1st round.
He's been a guy that was a little unsure mentally and is just now starting to realize his potential; which I think can still grow. Another year would really shape him up. Besides, if he ended up being the 4th or 5th WR taken, he'd likely fall into the 2nd round or have happen what has happened to many, e.g. Jason Witten.
Of course, maybe I'm just hoping.