So, with all things considered, should I just say screw it and have the Oldenburgs take the Polish-Lithuanian throne?
I think it would be an interesting path to take it down. Interestingly it’d both be a way to show how the events of your TL leads to changes in the rest of Europe, while simultaneously taking Poland-Lithuania down a surprisingly similar route as otl, with a foreign Scandinavian dynasty taking power. How you’d choose to resolve it is of course up to you, whether you see the PLC starting to decline in this era or have the Oldenburgs reinvigorate the state. How much of the Nordic-Polish relationship would be friendly and how much would be rivalry wouls also be interesting to explore.
Other commenters have suggested this as a vehicle for a Russia-screw. I don’t think it needs to be that just because we get a dynastic link between Scandinavia and Poland. Keeping Russia from ascending to its level of power it did otl would be a great way to keep Scandinavia as a major player, if that’s what you want, but this doesn’t necessarily mean partitioning Russia or anything - keeping it away from the Baltic shore would be enough, and might mean a Russia more focused on Central Asia and the Middle East instead. Way far down the line this could mean a more intense British-Russian rivalry, though it’s far fo early to speculate on such things. Either way, I don’t think a Nordic/polish conquest of Russia is either likely or desirable, it’s a likely way to overextend Scandinavian resources.