I think ut would be great if there would be new island in Simple planes like:
City Island - an island with about the size of Wright island but it would be mostly flat (there'd be some small hills tho, maybe a mountain) and there would be a huge city on it with an airport, factories a river with small bridges etc. and the factories as well as the bridges would be destructible (just like the ones at Karkaboa) so we can simulate WW2 bombing (the city would also feature anti-air flak cannons just like the WW2 destroyers in the game so it wouldn't be too easy to bomb it)

Junle Island - My other idea comes from my passion about the Vietnam War, this idea would feature a Vietnam-like landscape with huge jungles and some mountains, it woulld also feature a new type of AI enemy which would be very similar to the anti-air systems at the Snowstone base but these ones would only shoot simple unguided missiles so it would give the feeling that for example if you are flying low above the jungle with a helicopter they are shooting at you with RPGs, this island would also have like 2 airports and many small bases (with only helipads), the landscape would feature many hills and some big mountains

these are my ideas for possible future islands I hope you like it!