> Fil-C is more compatible in the sense that I can get CPython to work in Fil-C and to my knowledge it doesn't work on CHERI.

MicroPython has been ported though. What makes CPython special, so it couldn't be ported?

> Fil-C also has an actual story for use-after-free. CHERI's story is super weak

Indeed, CHERI does not always trap on use-after-free if the program is fast enough. A free'd memory object is kept until another thread has found all pointers to the object and made them invalid.

If I understood the paper right, Cornucopia-Reloaded does invalidate a capability directly when loaded if the pointed-to page is marked free. Therefore, any allocation of at least a page should have no use-after-free.