It's a good idea, and some sort of easily-verified compatibility with openssl was actually an early goal. But I gave up on that since the algorithms are so different. A compatible mode would end up sharing very little code, so it wouldn't say much about moochacha itself.

But good news! I've come up with... something.

https://codeberg.org/markdascher/moochacha/src/branch/main/o...

That strings together a combination of argon2 and openssl commands to decrypt a file. It's extremely unsafe though, since all of the secrets end up in command-line arguments. Also some of those commands might be new in OpenSSL 3.