I trust the authors immensely but i don't see what yet another class system in R solves. That's on me, but I'd like to understand more of what motivates this effort.
From the article: “S7 is a new OOP system being developed as a collaboration between representatives from R-Core, Bioconductor, tidyverse/Posit, ROpenSci, and the wider R community, with the goal of unifying S3 and S4 and promoting interoperability.”
It then goes on to describe what that means in depth.
It describes 3 new generics in base R that help their new S7 system.
It all seems motivated by better interop with python which is 'neat' but really doesn't seem like a critical necessity of the language. I guess it's more of a tactical thing where they're trying to make it easier for python users to eventually try R. Or for R users that work alongside python users to not abandon R.
The Python interop is in the blog post because it makes for convenient and compact examples, not because it motivated any of the features.
If you're interested in what motivated S7, you may enjoy this talk Hadley gave: https://www.youtube.com/watch?v=P3FxCvSueag (R7 was the working name for the package at the time)
It then goes on to describe what that means in depth.