Some might think about this as crazy but what about them partnering with WN on the American side for feeder flights it would greatly benefit both of them. WN passengers would fill Norse planes with them wanting to go to Europe and then Norse being able to have there passengers continue on to USA destinations they don’t serve
I would think that Norse would benefit from a partner short-haul network much, much more on the European side. They seem to want to cater largely to US-based customers who want to go to Europe for cheap, and these are the kinds of passengers who fly airlines like Vueling, Ryanair, Easyjet, etc on intra-European short-haul.
Even if they were to partner with an American lcc, it would most likely not be WN. WN does not fly to JFK or EWR so would be absolutely useless if they wanted feed directly from the NYC area intl airports.
However, an airline with a decently strong network at JFK/EWR, FLL, & LAX is B6. B6 is likely the "ideal" US feeder they are aiming for. Even still I don't see B6 pursuing any kind of partnership with Norse. In just a couple years, with the arrival or more LRs + XLRs, they will likely be competing in very similar tatl markets out of NYC that Norse will be interested in as well.
The next best option is NK. Decent networks out of EWR, FLL/MIA, and LAX. F9 has a more desirable brand image of course, but will no longer fly to LAX by the time Norse starts operations.
I still am unconvinced that Norse needs any kind of partnership with airlines in the West though. To me, the value comes in having a partner short-haul European network, where they can allow connections, since I presume that their services will be most targeted towards the US-based passenger. For example, I flew OAK-SPU on Norwegian in maybe 2018 and had a pretty seamless connection through LGW. Flew back DBV-OAK via OSL and had a similarly pleasant-enough experience. If Norse can kind of replicate the old Norwegian short-haul network, this time instead allowing connections on a separate European short-haul partner, they'll be golden.
Edited for grammar mistake.