However, thanks to some members of the community (burnpanck, who has python3 compatible (though not 100%) forks of parts of our core ETS stack, starting with traits, pyface and traitsui), this is slowly changing.
Based on his work, i have attempted to make chaco work on python3, and have largely been successful. The most significant changes were in the extension modules of enable, as expected, since the setup.py uses 2to3 to migrate python code. Enable's kiva renderer which uses AGG underneath, has significant amount of extension code. Luckily, most of it it written in swig which automatically takes care of python2 and python3 compatibility, though in one place i had to modify swig interface file for bytes<->str<->unicode madness. Chaco also has an extension module for contour plots which uses direct Python<->C api which i could make compatible with both 2 and 3 with some #ifdefs.
In short, migrating from 2 to 3 in not really difficult for most programs. 2to3 makes it even less effort, you just have to figure out the things which 2to3 cannot handle, which is easy if you have tests.
Current status: Enable and Chaco seem to work very well under python3. All enable tests pass, though a few chaco tests fail. Also, the chaco toolbar overlay seems to segfault. All other examples in the Chaco demo run very well.
The story is not as so good for traits and traitsui though. The traits `implements` and `adapts` advisors do not work in python3. They are already deprecated in traits, so you must use the corresponding replacements from the new `traits.adaptation` package, even on python2. The same work is also required to be done for traitsui, which uses the old mechanism in quite a lot of place.
Python3 branches of ETS components:
Traits : https://github.com/pankajp/traits/tree/python3 (derived from burnpanck)
Pyface : https://github.com/pankajp/pyface/tree/python3 (derived from burnpanck)
TraitsUI : https://github.com/pankajp/traitsui/tree/python3 (derived from burnpanck)
Enable : https://github.com/pankajp/enable/tree/python3
Chaco : https://github.com/pankajp/chaco/tree/python3
PS: If you are as excited about this as I am, please help the cause by using the python3 branch in your project (they also work with python 2.7), and submit issues and pull requests for both python2 and python2 compatibility. Thanks.