THIS OFFSEASON

I think the only way that the Kings do something like this is if they are 100% certain that they can't resign Doughty. If I were a betting man, I'd say he signs an 8 year extension in the offseason.

Also, what would the cap outlook look like? I know it'd be tight, since Matthews is getting somewhere around 11, Marner around 6-7, and then Doughty around 10 or 11 as well. Depending on when Horton's contract ends (I don't know off the top of my head), I'm not sure adding Doughty would fit under the cap.

You're right. That is the thing. They wouldn't fit Doughty into long term cap space. He would stay in LA. Just like Tavares would stay with Isles and Stammer stayed in Tampa.

Cap is going up though. Horton is nearly done, so Toronto would have roughly 30 million by the season’s end, Matthews and Doughty can take around 10 million, and Marner around 6.5, this leaves some leftovers for Kapanen and the young guys.

However, while it might be possible we would be tight on the cap. But if Toronto cannot acquire a big name D-man they will never win a cup. Gardiner is weak on the puck, Zaitsev is no more than a second pairing guy, leaving Rielly as our only real big name. We have great offence and solid goaltending, but Lamoriello needs to fix the blue line. Rielly, Liljgren, Zaitsev, and one other big name would have us set for a cup.

I agree that Liljegren is going to be really good for you guys sooner rather than later. But it's going to be tough to find another big name defenseman, especially given the cap situation. Maybe they have a defense by committee? Where they basically roll three pairings worth of #2, 3 and 4 defensemen and give them nearly equal minutes. Just in case they can't acquire a high end defenseman?

I'll agree, that Doughty might be able to fit under the Leafs cap this year in 2018/19. Not sure after that. But really there isn't 30m available, plays have to be signed, performance bonuses have to paid, and probably Hortons's cap hit has to included in the opening roster.
But I still don't see what is LAs motivation to trade Doughty next summer. He can still lead his team to deep Cup run. Good teams don't panic about upcoming UFAs leaving, they still try to win.
And realistically can't the Leafs wait to 2019/20 and see how the cap plays out with their players before making a run at UFAs, and there will be some available.