Chat channels are in, and working. They're more like the Diablo II IRC style than the individual chat windows like StarCraft II has.
Having ways for friends and acquaintances to create social groups has been in the long term plans of the new Battle.net for some time. Whether they're called clans or not is a smaller detail. It's just getting the time to work on adding in those types of want-to-have features. Almost assuredly not for the launch of the game, but hopefully at some point in the future.