Vegas makes a ton of sense. If they cap goes up to 80M as rumoured, they'll have almost 40M in cap space next season with 17 players already on their roster and Neal, Perron, W.Karlsson, and Shea Theodore being their only players to sign. Those players likely cost them about 20 million, so they'd still have roughly 20 million in cap space before adding Karlsson+Ryan.
If this is a situation where Karlsson has asked for a trade, and we have to move him, this could be potentially a good play for Ottawa if Vegas wants Karlsson bad enough to play ball.
Put yourself in George McPhee's shoes, if you could get a top 3 player in the game at 28 years old for something like Theodore+Glass+2018 1st+2019 2nd+2020 2nd, you've gotta do it, even if it means taking on Bobby Ryan.
A lockout is almost certainly coming in 2020, and that might mean another round of compliance buyouts. If that's the case, Vegas would only have to suffer through 1 year where Ryan's 7.25M cap hit overlaps with Karlsson's extension.
Assuming Karlsson has requested a trade, or made known his unwillingness to re-sign, packaging Ryan with Karlsson isn't a bad initial strategy so long as Dorion and emperor of hockey operations Eugene Melnyk are willing to roll with the punches if that kind of deal doesn't materialize. Asking for Ryan to be packaged with Karlsson gives the Senators a huge concession to leave on the table in a counter offer if that kind of deal doesn't happen.
Is it a coincidence that this news dropped right after Dorion was spotted on a plane in DET which apparently is a major hub to head to Vegas? Is this the kind of deal big enough that two GMs need to sit down in person to hash out?