Blizzard does not
support multiboxing in any game. They allow it. (As the first sentence explains.)
And you have to read into "some software
used to facilitate multiboxing may violate our policies", because obviously they are not telling you specifically what they mean and it is left open to interpretation. I am pretty familiar with Blizzard policy and we do not allow discussion here of said software that some people use "to facilitate multiboxing" that violates Blizzard policies. (hint: some people cheat, this is not really related to multiboxing)
There is absolutely no change in multiboxing status in Diablo 3. If anything you should be happy about this:
http://us.battle.net/d3/en/forum/topic/13140803986.