User of Ruff here and follower of Charlie's work.
I've been slinging python since 2003, and I've used a pretty wide swath of the toolchain. I've also had the (pleasure?) of using python in a lot of different contexts: desktop applications, web programming, custom scientific calculation plugins, grad school hacks, Maya, and obviously Juypter notebooks.
My honest take: Toolchain tools like Ruff are the only way the Python ecosystem as a whole moves forward. In order to be broadly adopted by the wide swath of use cases, it needs to be universally applicable and have a killer reason for being (in this case, speed, which opens up new use cases that didn't exist before).
Ironically, the commonality to these toolchain improvements for python ... is that they not be written in Python. If you want good analogues, you can look at the work that others have done with multithreading and trying to bypass the GIL, which is one of my other hobby horses with Python. Hot take: For most users, python is not used for itself, but more to flexibly orchestrate some other low-level problem. This is why Maya, scipy, most of data science, and other DSLs use python so much.
To empower these users, you either need to (1) work in the compiler (2) below the GIL or (3) do the heavy lifting of wrapping around the language flexibility without requiring changing the python code itself. Ruff does that, and I imagine the thesis of Astral is to extend that philosophy to the rest of the toolchain.
Lastly, in the spirit of this site, I'll give my second spicy take: I think web development in python is on the decline, and the future of python is in data science and related fields. These fields care a lot about fast toolchain, and will use ruff and other tools to achieve those ends without modifying legacy code. For web, node has won. I know users that use python but you can't really beat needing to learn just one language vs two to build a web app.