My group has taken the ultimate step that many on this and other sites are loathe to do. We have unified turns, 1:Axis 2:Allies. We mainly play a modded AA50 with slightly (5-10) more territories. This greatly increases the speed and playability for several reasons.
Firstly, the vast majority of the engagements can be done simultaneously without any real issues.
Everyone can purchase simultaneously, and if you are not particularly a-retentive some people can finish their purchasing while others are moving forward with their attack declaring, but please make sure all attacks are declared before any attacks begin, to easy to start conflict there with meant-to/didn’t-do.
The most important factor in time improvement is not the actual simultaneity of the turn but that every turn, every round, attack and defense, involves every player. No one is bored (US/USSR) for turn after turn of waiting to do anything. This engagement greatly increases the camaraderie (heh) and the pressure of the turn. Everyone’s attention is focused. We REGULARLY complete our AA50 to a satisfying surrender in about 3 hours. In fact most of us have young kiddos so we don’t really have a choice.
Another useful point is that if someone brings an uninterested significant other or newbie, Italy makes a great and dynamic option when coordinating with an expert playing Germany. I find that scheduling is one of the hardest issues with getting a group together and perhaps one of the main reasons you would want a shorter game.
No 1/2 punches with Italy/Germany or UK/US. This might be a bigger problem on Global but I do not feel that it is an issue in AA50. To correct this we use some special rules including a reserved 2nd attack round for unused armies that want to attempt a blitz through/drop past a recently conquered territory or Sea Zone.
Massed Allied navies, especially in Europe. Haven’t really figured this one out, but it is historically accurate and axis can usually get the allies to a surrender point without Operation Sealion anyway. Massed navies is one of the reasons we support the 7/0 Transport rule in the recent editions over the 8/1 of the old editions.
Starting positions for UK and USSR. Since Axis will move collectively ahead of them, USSR and UK might need a little tweaking in the setup. I usually move some of UK’s Pacific/Indian navies one space further from J1. Additionally we give a territory or two to USSR to absorb the assault of G1.
I feel like if you really want to make A&A work for you, it can. It just might take a little more willpower in working through and agreeing to some compromises on OOB rules.
P.S. It always helps if the scheduling problem is with other people, you be the one to set up ahead of time. I always end up falling on that sword.