You may enjoy this breakdown of type I-II-III remailers: https://elly.town/d/blog/2022-02-09-mixminion.txt
I have considered porting mixminion to Go and implementing it as designed.. it's pretty interesting. I think it would be neat if you added "bridges" like an SMTP -> Mixminion and Mixminion -> IRC/Matrix/etc.
Of course, you could chain something like Mixmaster -> SMTP bridge -> Mixminion or Mixminion -> Tor -> IRC/Matrix/etc.
edit:
I submitted the URL to HN as well.