Going from 6 division to 4 conferences is a radical change. But the Leafs' current division remains largely intact with the addition of the two Florida teams. The Leafs will play 6 games per team within the conference and 2 games per team outside the conference. This will result in more travel but more visits to the sunshine state in winter - how bad can that be.
An earlier realignment had Philadelphia, Pittsburgh and Washington in place of Florida and Tampa Bay. Had that been accepted it would have been quite the challenge to make the playoffs with the toughest 4 teams in the East all together in one conference.