The risk with such rewrites is ending up with a Python 3 situation and an ecosystem split. Sounds like YARA-X is (mostly) a stricter subset of YARA, and it's easy to write rules that are valid for both:

https://virustotal.github.io/yara-x/docs/writing_rules/diffe...

Although I wonder how long it'll stay that way? It'll be very tempting to add new features to YARA-X that won't be backported to YARA.