The semantic change actually needed to make nested() more equivalent to the multi-with statement is for it to accept zero-argument callables that create context managers as arguments rather than pre-created context managers.
It seems to me that both passing callables which return managers and passing a generator which yields managers achieve about the same thing. Are you proposing the former just to avoid introducing a new interface?
Rather than changing the name of the function, this could be done by inspecting the first argument for an "__enter__" method. If it has one, use the old semantics (and issue a DeprecationWarning as in 3.1). Otherwise, use the proposed new semantics.
I guess this is much too late for 3.1, but could we then at least un-deprecate "contextlib.nested" for now? As it is, you get a DeprecationWarning for something like with contextlib.nested(*my_managers): without any good way to get rid of it. - Hagen