So if the next version of AIR is going to use Squirrelfish, does that mean Adobe will contribute ActionScript language features (packages, classes, method/property visibility, etc.) to it?

By the sounds of it, ECMA's going to end up irrelevant—even though they rejected ECMAscript 4 as proposed by Adobe, all of the runtimes will likely end up with support for all of the proposed ES4 features *anyway*. Possible exception of Microsoft's, but Adobe could possibly pull a clever trick in bundling a WSH engine along with the Flash player to render this moot.