Is there a known date/timeframe when python 2.7 will not be supported any more in favor of python 3?
In May 2010, Word of God was that patchlevel releases for Python 2.7 will probably be made for at least 6 years.
So, maybe 2016, probably later.
Edit: Pushed back to 2020. See the revision to PEP 373, linked to in other answers.