I think an interesting question for any airline wanting to do an FPP-style programme has to be "who's going to provide the loan?" now that BBVA have exited the pilot market and seemingly no-one else wants to enter it with a bespoke product. People can remortgage their own/parents homes with their own mortgage provider however an airline would need a company to provide 50-100 loans all on identical terms, basically a bespoke product.
I do wonder if in future it will be up-front from the airline (i.e. Aer Lingus from recent times) or no funding from the airline at all. Of course, an airline as guarantor may tempt financial firms back into the market.