Karlsson is currently making 2m in real dollars, and his upcoming signing bonus is only 1m. From a cashflow standpoint, it's actually a good time to make a deal for Karlsson, seeing as new ownership could pick up the tab as he becomes costlier.
And this year, Chabot is making only 4m in real dollars, while no other defensemen here are making more than 3.25m in real dollars (other than Zaitsev at 4.5m of course).
So long as retention (say 25%, so 8.6m cap) is part of the salary structure for Karlsson moving forward, and a few pieces are moved around in the offseason, it's actually doable to acquire him now without paying salary out the nose for our defense corps this year. And a note, I think if we ask for any more retention, we have to part with too much the other way.
That said, Chabot and his 8m cap goes up to 8m in real dollars next year, and 10m the year after along with a 10 team NTC. Meanwhile, although Karlsson's bonus is 1m next year, his salary will be 10.5m, which, if 25% is retained, will be in line with Chabot at 7.9m.
So, a decision would likely have to be made about going all in with heavy dollar and term investments to both, or flipping Chabot to address other needs before his trade protection is enacted.
Re-acquiring Karlsson and his NMC for 4 more years is a full blown commitment to the player, and I think that aside from the short term Zaitsev problem, having to choose between Karl and Chabby for the upcoming contention window is the major dilemma here.