Dan,
I know these kinds of things are a hassle to run down the legwork for, so I appreciate you chasing it.
While a 20" AUG in the collection would be cool, I think if I had just one it'd be the 16". As Paul noted, with the barrels being pretty pricey, slapping in a 16" later isn't cheap/easy (even if it is technically very easy with AUGs). Especially if the 16s are hard to come by, I doubt a lot of extras will be available outside of complete guns. A 20" AUG is still a really compact gun, though...
The one thing that might keep everyone's interest is if this was a great deal of some sort - I don't suppose Pete gave any indication of what a price for such a package would end up at, did he?