Guido has now accepted PEP 3119: Introducing Abstract Base Classes. The discussion on this topic went on for a while; so long, in fact, that it led to PEP 3133. But in the end people were either tolerant of the PEP or liked it.
Personally, I am indifferent. While I provided feedback on the first draft I honestly have no personally need for this. But I do know people do request we have some way of specifying interfaces (or something similar) fairly regularly. At least we have an easier way to tell if you are dealing with a sequence or a mapping data structure.