Splitting Python 2 and 3 as filetypes in Geany is whole another story. Apart from the fact, that I don't think it's necessary at all. Except a very few details, the syntax is identically regarding highlighting between Python 2 and Python 3. And in the long term, most people will write and maintain Python 3 code.
Back to this issue: I'd say let's way for Python 3.7 and then just regenerate the keywords list. In the meantime, users can manually add the keywords if necessary.