So many issues with this proposal. The main ones being:
1. Trouba wouldn't want to re-sign on a bottom feeder team like Vancouver.
2. That 2019 1st rounder would be top 10.
3. Why would Winnipeg replace Trouba with Tanev when Trouba is 4 years younger and Winnipeg will be a contender for many years to come?
Your proposals never take into account team needs.
1. You get to lead the defence and the team should improve greatly over his term there.
2. They can protect it for top 3 or something. It would still be a very valuable chip, possibly for the Jets to go and acquire a star player at the deadline.
3. If Trouba won't sign for a reasonable amount </= $6.5m per, then you should trade him. He really isn't that good. He's basically a healthier, younger version of Tanev, with some offensive upside. Vancouver is at a place in their rebuild where it makes sense for them to overpay a player like Trouba, it would be foolish for Winnipeg given the better uses they have for their money.
If I'm saying no to this as the Jets, it's because of concerns that Tanev will get injured. It's not because I think there's much of a quality dropoff there.
If I'm Vancouver I would insist on using a set of second rounders instead of the 1st, too risky to use the 1st.