The Blackhawks are likely not ready to move on from Jones just yet. They probably want Vlasic and Korchinski to get at least one more year of experience before moving out Jones, and if they become a playoff team quicker than expected, they might just keep Jones long-term.
The Maple Leafs are likely not ready to add a contract like that on defense until next summer when Tavares comes off the books. I could see an exception being made for signing Brett Pesce to a long-term deal on July 1st, or trading for a total stud. The cap structure of the team might make it make more sense if you're moving Marner out, but I think (a) we could get a better return for Marner, and (b) Chicago won't want Marner unless they can extend him long-term. They wouldn't be able to just add him and move him again at the deadline as a rental easily, as he would still have his NMC.