This would be a clear case of selling low.
He's a classic case, IMO, of how NOT to develop a young player. Throw him into the NHL at 18 when his body and game was clearly not ready, he gets injured and gets low ice time. Year 2, as a 19 YO, he shows improvement, but is still frequently over-matched when forced to play top 6 RW (when he's naturally a C). Year 3, he again is mainly used either on the top line RW or 2nd "shut down" line RW and just does "OK".
That said, some of it is clearly on him as well. For 2 straight seasons, he struggled out of the blocks (1 point in 11 games this October). He's skilled, but his skating and lower body strength hasn't been good enough to utilize that skill. He's not slow, so that, to me is a case of him working in the off-season to improve it. He hasn't been fast enough to blow by guys and hasn't been strong enough to shield guys off (like Rask does). Brind'Amour even called him out a bit at the end of last season saying that if he wants to be elite, he's got to put in the work off ice.
All that said, he's only 21 years old and basically has two 40point (ok, 39) seasons under is belt. Based on reports and videos we've seen, he's also taking his offseason training much more seriously working out with Nik Backstrom under Andreas Öhgren.
https://novacapsfans.com/2016/07/08/andreas-ohgren-on-training-backstrom-and-other-nhl-players/
I think he'll come to camp prepared and get a chance to play center between Aho and Teravainen. I personally expect a much improved season from him, provided he stays healthy. I have high hopes for him this season.