If there is an interest from the legacy carriers to keep 50 seat flying after 2030ish I think they will start building them again in some fashion. We have to keep in mind that Boeing has big airplanes to sell so they have the ability to scale pricing up and down to be able to make a profit on one jet order if they commit to order another at a loss of profit as long as an overall profit is made. We will see how it works out though. I personally think that as long as the economy holds some what and travel demand keeps growing the new 50 seater is dead unless we go with a turboprop like the the ATR which legacies hate.