Do we know how much more it's likely to cost? I could easily see people paying 1.5x - 2x.
Anything beyond 2x I imagine would start to price out the average person and anything beyond 5x would probably price out the vast majority of potential customers.
People pay more than that for domestic first class, which doesn’t even have lay-flat seats. $2,500 or even $5k for a New York <> San Francisco 2-hour flight would absolutely sell.
They're limited. And I regularly see them going for $4k+.
I don't know if those theorized efficiencies will be delivered (a lot depends on that engine) or if airlines will price tickets at that level. But it's the theory so far.