Have you checked the issues for a similar suggestions? Yep

How would you improve Rich?

I want to use a custom spinner animation (not just one provided by rich. I can see that there is a consistent format for these, and so accepting custom spinner definitions would be a relatively simple improvement. In fact, I'm happy to attempt implementing this myself.

What problem does it solve for you?

It means I can provide my own custom spinner animations, which will make me happy.