It's pretty cool all the stuff from the highlights I saw Zellweger do in WHL & AHL he's doing the exact same things in here. That skating/transition ability alone guarantees him a spot in the league, but the sky is the limit for him since his game is just made for the current NHL.
His awareness of player spacing is a huge asset for him. I think it's an attribute that isn't talked about enough. Guys like Getzlaf, Nieds, and Pronger had that awareness pretty much sky high (along with other elite attributes, don't get me wrong) and they thrived in the league (partially) because of it. (I'd also add way after the fact that it's all the more impressive for Zell given how much faster the game is these days)
He just needs to get a better sense of the right time to cheat in offensively and when to get ready to swing back on defense. Thought he had a couple really good defensive plays last period so I don't think it's a question of whether he can do it, just knowing when the situation calls for responsibility and when it calls for some risk taking.