While I don’t know the timing of the releases, I would assume since the 4.4 builds are on RC2 currently and there’s only about a dozen items left on their JIRA marked as 4.4 Required, I would assume that the release is only a few months, at most, off. That is purely a guess however based on what I see.
I don’t think that MongoDB provides estimated release dates either, but maybe someone on the inside will come by later and give a more official answer.