There is a port in the works [0], and apparently they decided to go with a rewrite instead of just a port. I'm not sure of the exact reasoning, but that could explain why it takes them time.
There has certainly not been a lack of work on porting, there was the neo branch as well, there is some interesting (for some values of interesting) discussion about the approaches to 2.x and 3.x compatibility:
I don't know all the backstory, but when I pip-installed awscli in a py3.4 virtualenv this week, it pulled in "botocore", among others. Everything seems to work fine, so at least botocore works on version 3. Since awscli is a very complete AWS interface, it may be just a matter of documentation or a very thin API layer before everything one needs in boto works fine on v3.
