To me, Trouba likely wants to be the alpha dog on d, at some point. First unit pp, pk and play 25 mins a night.
I think Trouba wants to be the man, and the rewards that come with that. If, IF, he's disgruntled in Winnipeg, it's because there are players in his way from being "the guy".
Right now, the Jets have Buff in that role. Will be in that role for at least 2 more years, until his full NMC lifts. At that point, a Buff move is a possibility.
It may be in Trouba's best interest to bridge for 2 years, see what happens with his own development and playing time, and whether he surpasses Buff in effectiveness. Should Trouba develop into a legit top dman on the team, then you can pay him accordingly and move Buff. That would be when a long term deal is best for him in maximizing dollars, the PK Subban example. Otherwise, Troubs is making $5mill and playing like a $9 mill player.
If I were the Jets, I'd go 6 years at $5-$5.5 mill, with Trouba and know for most of that contract he will be outperforming the annual value.