There are narrowbodies across the Atlantic though, the question is how low can a company like ryanair price say a Dublin -> Manchester NH flight to ensure they can fill a flight connecting New England to Ireland.
But they don't operate that type of route with existing planes, not sure how the extra range would help.
It could open up a new industry specifically for this purpose. Right now for narrowbodies all transatlantic routes are pretty marginal in terms of range. There are some but only on very specific routes, which doesn't scale (you don't buy airliners for just one route because you'll have a huge problem if you need to change it).
And Ryanair is an Irish airline but Ireland is far from its main market these days. For the rest of Europe it's already a lot harder to reach with their aircraft.
There are a few lowcost airlines already targeting this market, like "Level" in Spain. They had to scale down long-haul destinations significantly since Corona and I could imagine smaller capable aircraft could pick these back up.
I live in a smaller city in Europe that could really benefit from such destinations.
But a ryanair, or ryanair style system, could fly from a large part of the US (certainly the east coast) to a large part of Europe already without the XLR A321s. What new routes does it really open compared with the A321LR?
But they don't operate that type of route with existing planes, not sure how the extra range would help.