Ihave had a few suggestions pop into my mind so why not write them all down here:

1) better cockpits. Right now, cockpits are basically invincible cameras, and perhaps adding a system where you can make custom cockpit layouts, I.E be able to add a heading indicator, nav sphere, course deviation indicator, altimeter, spedometer, among other things to a custom cockpit. You could also make buttons that, when pressed/clicked can activate a specific action group. I think this would make the game much more immersive and add challenges like where to put the cockpit in the first place to improve visibility. This would also give the cockpit blocks a different use aside from being cosmetic. Its simple, two cockpits combined, double the space to put instruments/buttons. Also, this would allow several new branches to opened for the game. For instance, VOR navigation could be added with a course deviation indicator part, or airport ILS. This could also be easily transferred to mobile as anything clicked could just be tappable for mobile users.

2) toggleable ATC. adding a rudimentary form of ATC, like having to request to land/takeoff/taxi to specific locations could be pretty cool and exciting for more serious players of simpleplanes. However, for those who aren't as serious about it or just don't want to have to deal with ATC can turn it off, so this new feature doesn't become a huge nuisance.

3) commandable NPC planes/vehicles. This could add some really cool things to do in simpleplanes. Want to fly a 7 plane formation? How about a 50 bomber assault on the dreaded kraken? This doesn't even need to be exclusive for aircraft, you could spawn in more U.S.S Beasts/tiny's or other destroyers to either land on or attack at ones leisure.

4) be able to switch off that goddamn missile base in avalanche. Avalanche island, in my opinion is the most beautiful island in the entire game, but its wasted by that missile base. Imagine being able to peacefully fly a bush plane in and around the glaciers without having to be worried about getting shot out of the sky. I really wish I could fly the bush plane or maybe one of my general aviation aircraft replicas around the mountains and rivers of avalanche, but I can't because of that missile base. (and yes, I know if you spawn in the base the missiles wont shoot you, but its hard as h*ck to get in there in the first place)

5) an actual airstrip for maywar. Now I understand that Maywar is sort of supposed to be like a desolate desert with only ancient cities (and wind farms) on its surface, but maybe a small airstrip with a hangar could still fit the asthetic of maywar, especially if you put it by the ancient ruins.

Thats all. I know pretty much all of these were rather.. outlandish, but please maybe think about them? I think that if just one of these suggestions were added to simpleplanes the game could get even more enjoyable than it is right now.

TL:DR: customizable cockpits, toggle-able ATC, command-able NPC vehicles, making avalanche more friendly, actual airstrip at Maywar.