That's great that you use NLTK3 and Python 3.x and it works fine! There are no known Python 3.x incompatibilities. But if you find something then please report it.
Issues that prevent a release are not related to Python 3: check https://github.com/nltk/nltk/issues?milestone=2&state=open, https://github.com/nltk/nltk/issues?milestone=3&state=open and https://github.com/nltk/nltk/issues?milestone=1&state=open.
I suppose they're not officially releasing it because there may be some unloved corners of the library that don't work yet on Python 3. But everything I've done with it has worked fine.