Nylander isn't being traded for a top-4 D. There is no way a guy who scored 8 goals and 32 points in 50 games in the AHL is replacing Nylander, unless your goal is to enjoy a permanent rebuild hoping to draft more players as talented as Nylander. Let's try to remember that Bracco is only 10 months younger than Nylander. And 61 points has been Nylander's lowest full season total. No reason to believe it won't be upwards of 70-75 as early as this season.
The Leafs have a top-4 (possibly top 2) RHD in the system already in Lilegren. The smart money says you look for a stop gap veteran top-4 on an expiring contract to pair with Rielly for this season, and push Hainsey to the bottom pair where he will get less minutes allowing him to PK all night long.
The Leafs have a lot of younger promising D right now in Borgman, Rosen, Sandin, Durzi, Rasanen, even Holl, etc....blowing their brains out for a D-man at this point would be a dumb move IMO.
The Leafs were 3rd out of 16 teams in the Eastern Conference in GA, only 2 GA out from second. Better than Washington. Better than Tampa. And they got rid of the defensive black holes that were JVR and Bozak, and have replaced them with Tavares and the likes of Johnsson and Kapanen. A clear upgrade on the D without even touching it because the days of being hemmed in will be gone. Tavares excels at zone exits. Bozak and JVR couldn't execute one to save their life.