The Phase One Box set DVD/BR is still coming....it's just going to be Spring 2013
and now with slightly redesigned case.
...the Phase One set will indeed see a release, albeit next spring instead of later this month. SuperHeroHype has confirmed that case design will change, although we're not yet certain exactly how significantly. Check back for details as they become available.
This is still favorable as they can now tie the release into the launch of Phase Two with Iron Man 3
likely weeks away with it's May release. Assuming the set is released in April. Plus it increases the likelhood of more double dipping. If you were just going to get the set in September you probably weren't going to get the single disc or 2-disc set even. Now though, with a 6 month or so gap the cash-in on double dipping is back in play. Even though you could argue they weren't going for that by timing the set release with the single disc release. It's a win/win for them.