It appears to be the ability to 'upload' or match new songs and then have them wirelessly sync over the internet to all of your devices would disappear. AAC doesn't have the ability to 'expire' content, as far as I know?

Apple’s DRM container files used AAC encoded audio. (This service seems to be without DRM, though.)

Yes, but the iTunes music store has been rid of those for a while, and like you said, they've specifically stated that these will be DRM-free.

Most likely your converted music goes away(music you didn't buy from iTunes) from the cloud storage. The music on your harddisk isn't going anywhere.

I guess the question is: When I upload something to iCloud, does that actually get synced to all of my devices or do all these things just have streaming access to iCloud? If it actually syncs all of the files, do they go away from all but the original computer after the service is terminated? I.e. if you use this to convert pirated files to legal AAC, do all of the synced AAC files disappear, leaving you only with the original pirated MP3s when you stop paying Apple?

I'm wondering this too although it's a moot point since iTunes Match will be (yet another) U.S.-only music service