We're planning to upgrade AIW to Unity 4 a month or so after 6.0 (the AS expansion official release), as the 6.1 (or whatever) official.
Unity 4 removes PowerPC support, and while that's not a lot of our customers we wanted to get another official out that they could use before doing the upgrade, and there wasn't time to get it stable enough for that before the expansion (largely precisely because expansion work is ongoing).