It's certainly niche, but NY-LON sees ~3 million non-connecting passengers a year.

If they can make it quiet enough to be supersonic over land, it's a lot more compelling. But even being supersonic for the atlantic crossing will shave hours off of most EU routes from NY.

I think the bigger problem is the time changes on a lot of routes make EU flights pretty efficient - you don't want the overnight flights to be shorter really (and I wish most were longer).