Since we are on this topic, I have been toying with the idea of an AU also. Particularly a WW2 German FD scale AU. Not too sure if it is entirely viable but here are a few basic ideas after a bit of research (and in no particular order):
Gradual increase of (total war) production prior to start of WW2 (peak production of aircraft could be reached ~1941-2 rather than Mid-1944)
-->Aircraft Industry left to own devices, therefore more planes produced from 1936-'42 than in OT
Delay in attacking Poland/Britain agreeing to peace which would
Development of more effective radar earlier on
Jet research has more interest
--> He-280 sees operational combat while Me-262 is being developed
Strategic bomber force built up in the '30's (General Wever doesnt die in crash)
-->Ernst Udet replaced by Erhard Milch
Due to increase of production more powerful engines are brought into service quicker (Jumo 213, etc)
Technical advancements:
-->X-4 and R4M brought into full operational status
This AU will probably be a longer, bloodier WWII, but there is a lot more to take into account before I start obviously!
Just trying to get the technical stuff down since the whole AU idea fascinates me, anything that should be noted will be gladly taken into account of course! But if I can't get an entire AU worked out I'll just draw what I can.