Here’s an idea for an aircraft restoration mission.
There’s some vintage aircraft parked at Prague, so I thought that they should be able to be restored for your fleet.
You could do missions, such as flying a specific route a specific amount of times. For example, to unlock or earn a free Concorde for your own fleet at Prague, a possible achievement could be to handle 50 Prague - London Heathrow flights.
For Nagoya it could be the 787-8 at the Flight of Dreams exhibit, so 25 Nagoya - Seattle flights.
I’m not sure about how this could work at other airports, but a historic visit or the first flight from that airport could work.
It’s a dumb idea I came up with in 5 minutes, but I think it would be cool for veteran players that really have nothing else to do.