He's got a lot of potential as the prototypical modern defenseman. Mobile, smart, likes to have the puck on his stick, and sound defensively.
That said, it's tough for me to say I definitely see a future #1 there. His offense benefits a lot from the lack of structure in the CHL and playing against much less talented competition. I don't think he'll be quite as dynamic when he breaks in. Fortunately, his defensive fundamentals are sound, and after he gets broken in I see him being a reliable two-way workhorse on the top pair who can punish teams who try to shut down Makar, but maybe not ever a guy you would love to have as your #1.
A lot will depend on how much of his offense translates, and how quickly he adapts to NHL speed when he's defending. I expect his rookie year to freak people out because it will be up and down, but given time I think he can be a strong #2 and excellent yin to Makar's yang.