They have clearly stated that any long-haul airline would be operated completely separately from themselves. And I, for one, don't think that will change.
The lower fares to the US east coast is about £470 rtn inc tax
Only those kind of prices during the all-important summer, when demand rockets and fares soar. During the winter, however, prices plummet; indeed, during those months it's possible to get London-NY-London including taxes for about £200.
I wonder if Ryanair themselfs are thinking of this route
as a feeder route
FR will never offer proper connections, with through ticketing, connecting baggage, increased responsibility, etc, not least because it results in greater complexity and reduced yields. But what would be possible would be to fly into one of their bases with the new, separate airline and to then connect manually: get your bag, go through immigration, then check in again. You can, of course, presently do this, and I have done it. It revolves around consumer responsibility: it's entirely your risk. It doesn't decrease airline simplicity or result in lower yield because you book flights separately. For example, if you were flying PIK-STN-SVQ you'd have to book PIK-STN and STN-SVQ separately. So, yes, you'd be able to manually connect from a long-haul flight to a European service.