At some point, yes, we'll drop Python 2 support. When really depends on how rapidly we see adoption (from users and re-distributors of Django) and how heavy the dual-version support burden turns out to be. My guess is what we're looking at a longer support window than the 2-3 years you posit, but that's really just a half-assed guess. Anything between "next year" and "never" would be a reasonable guess too...
... and y'know, Python 3 should be on your radar, if not necessarily what you use right now. It's better than Python 2 in every way (except for adoption, and that's changing). 3.3 in particular has a ton of really great new stuff (futures! working namespace packages! yield from!) that you'll wonder how you lived without.