The Hawks are a bad team to use as an example in the OP, since they are the team that would benefit most from Dahlin's ELC, and they probably could not afford to add Karlsson at 10.5-12.5 million. Dahlin will be locked in at about 4M after bonuses for the next three seasons.
With that said, I think there are some teams where Dahlin for Karlsson would make sense. A big consideration is that if a team has significant cap space now, and thus won't benefit from Dahlin's ELC as much as a cap strapped team like CHI would, in 3 years when the ELC is up, Dahlin won't be all that much cheaper than Karlsson. Look at the Ekblad extension @ 7.5M and consider that the cap might be as high as 90M by the time Dahlin's ELC expires. If Dahlin pans out, he might command 8M-10M on an 8 year deal straight out of his ELC.
There's also no guarantee that Dahlin becomes as good as Karlsson. Being a defenseman and not a forward, it becomes harder to project development perfectly.
It's hard to find a team that would be a good fit. Maybe the Rangers. They certainly have the cap space, and even if they intend to further strip their roster, the addition of Karlsson would give them a legit top 3 player to expedite their rebuild.
The Sabres are another one. Sure, Dahlin would be a great addition with Eichel, but would they really turn down the #1 RD in the game to play with Eichel? They have struggled for the last few years, and adding Karlsson could be a game changing move for them.