“Readable” code is more dependent on the author than the language. Many people can write completely unreadable code in any language.
We will continue to support all of the languages that we currently support in Rhino. Support for different python runtimes is not a matter of replacement of one python for another. We can find ways to add support for additional runtimes.
If you want to use CPython 3 and Rhino, you can do so today with the ‘rhinoinside’ project. Rhino inside Python