The straight rules, and IC building on islands would top my list as well. A very limited NO package would be ok with me, and yeah convoys (ohh boy here we go LOL)
I think it might be possible to to add both air & naval bases to the game (very limited). Start with placing AB/NB at ICs (where applicable). Wouldn’t give them any movement bonus BS, but allow 1 unit to scramble from an AB, and ship repairs need a NB (maybe even consider 2 hit carriers?).
Could put NB’s in key areas like Haw, Carol, Phil, Gib etc… AB’s in France etc…
Could also say mobilizing air & naval units need an IC, and the appropriate base.
I wouldn’t mind seeing a house version that included the Chinese and Italians.
Just as an after thought, could maybe look at using the old AA guns for amphib def (art bunker?) These old relics would stay with the territory (neutral color) maybe fires a pre-empt kill shot at 2 every round (opposing casualties don’t return fire). It could be used to soak a hit, but if damaged then it no longer fires its pre-empt shot (doesn’t fire at all). It is never destroyed and if territory is taken it stays in tact. Only one per tt allowed, and after the battle it auto repairs (damage removed), regardless of who ended up with the tt. Not sure, but maybe allow these art bunkers to be built in any territory, and place some at set-up?