We are a year and a half to Python 2's end of life:
https://pythonclock.org/
The number of Python2-supporting development tools and useful modules, used in the development and in user extensions of Calibre, will reduce considerably:
http://python3statement.org/
Would you be interested at least in supporting both Python 2 and Python 3? There are ways to do it in a reasonable amount of effort.
https://docs.python.org/3/howto/pyporting.html
There is also a way for you to apply for financial support from the PSF!
http://www.getpython3.com/#financial-support
I am also very eager to help, in whatever way that I can, as I use your wonderful program on a daily basis!