What's in the Flash 9 AS3 that's not in the current Alpha F9 AS3?
The release of Flash 9 seems like a long way ahead (summer 07?)
so I wonder wondering what's taking them solong and if Adobe is working on anything that might change/add to the actionscript language/API.
Is it a good idea to consider the alpha build as very close to the retail AS3 spec?
As far as AS3 goes, that really shouldn't change much at all. AS3 was defined for the Flash Player 9 and that was released with Flex 2. Flash 9 itself, the IDE, is just an application that will help you develop content for Flash Player 9.
When Flash 9 is released I doubt the language to change at all. However, it will probably ship with a lot of extra classes. I'm guessing they're currently rewriting the Flex mx package for Flash as it doesn't seem to work in Flash 9 without some tweaking.
Who knows maybe they'll add some goodness to it - mx2.graphics3d anyone?