I'm a little late to the bandwagon, but here are some suggestions I have for 1.8.

• Another Island
• Better graphics for mobile
• More parts, such as glass, hollow fuselages, etc.
• More weapons, like naval/tank cannons, nukes, etc.
  Better sky graphics (you can go above the clouds, more detailed skies in general.)
• Better weather mechanics (when you set the weather to "Overcast" or "Stormy" it'll actually start raining, or snowing, if you're at Snowstone. Things like storms, with actual thunder and lightning would be cool too.)
• Vapor cone when you brake the sound barrier
• Better Ai functions

Those were the "probable" suggestions, now for the "will never be added in a million years but just might happen somehow" suggestions.

• Make the hanger at Wright look better
• I REALLY want a loop at Skypark, it be so much fun for cars to screw around with that!
• Make multiplayer an actual default thing in SimplePlanes.
• Natural Disasters, such as tornados, tsunamis, hurricanes, and even the volcano erupting at Krakabloa, to randomly occur at any given point in time.

That's all, I'm sure that barely any, if not any of these will get added, but they're only suggestions.