Jonathan,
Maybe you should inform crew at Mega65 about this exciting project. It seems that people are pretty much active there (and in search for software tools for that platform).
Mega65 should be released this year iirc, and it should be downward compatible to C64. Think about it like Spectrum Next vs classic Speccy.
Links: Mega65.org , forum (games & apps subsection)
Thank you for your efforts.
Best regards