flufl.enum was the initial candidate for PEP 435, but the current approach changed and uses implementation techniques not available in Python 2.7

We may create a almost-compliant back-port for 2.7 as an external library though

You sure it's not better spending the energy elsewhere? Python 3 needs more exclusive features to encourage people to migrate from Python 2.

"Almost compliant" would mean compliant except for guaranteeing the correct order of iteration, would it not?