The next update isnt necessary the folloe update, its mors on bucket list and is not necessarily the highest on my priority list :p . However I would not be willing to increase willingness to pay, this is for a few reasons:
1. The game is already too easy imo, this would only make it easier.
2. I had considered adding full inflation model into the sim some time ago, but opted against it as I dont want to add a chore to players constantly having to increase prices to account for inflation. Its not fun for the user.
3. I want to make the sim more about broader management, like fleet management staff, strategy etc and move away from having to make constant micro adjustments to flight prices.
However to address your concerns, the fuel prices are currebtly adjusted for inflation, and the increases are as well. Yes, prices for fuel increase over time relative to willingness to pay, but that is also realistic and an issue airlines IRL have to deal with (hence airlines always looking to maximize fuel efficiency). In the future years the fuel increase does stop (I forget the exact year, I want to say 2030 ish), with the new model price will still fluctuate around that and in the old model it will be flat.