He's got a very good shot and he moves the puck well enough, but I don't see Chara potential, though to be fair, I didn't see Chara potential in Chara when he was 21 either.
If I had to guess, I think he's capable of 10+ goals a year and 30 or so assists. Assuming he gets a bit of PP time. Certainly would be happy with that.
I think Ceci has potential for more offensive upside than that, but he's so young I don't know if any of us can give a reasonable prediction.
Weircioch has finally developed but I think he's a wee bit behind the other 2 (and obviously considerably behind EK) in terms of offensive upside.
Edit: and I said this before, but if he keeps working on his shot he'd be a great pairing for Karlsson on the PP. Karlsson can clear a ton of space for him to let it go. He just needs to be able to be effective with it (i.e. the anti-Kuba).