> Another issue that I've encountered is that ASCII art becomes gets flagged.  Switching to a raw string then kills the unicode escape sequences.

If you already use escape sequences in your ASCII art, what is the problem of using them for backslashes?

> I think anyone who starts using 3.8 on a daily basis for non-toy examples will constantly run into this.

What is a better solution? The deprecation warning was emitted starting from 3.6. Deprecation warnings were silent by default in 3.6, but they become more visible in 3.7. This helped some projects (which give attention to warnings in they tests) to fix real bugs. But it was not enough, so other bugs are fixed only now, when the warnings become even more visible in 3.8. We see a value of warnings, they help to fix bugs. If we rollback this change, it will cause yet undiscovered bugs be hidden for more time.

In Python 3.0 we make many abrupt breaking changes at once. People complained. Here is an opposite example of very gradual change: two releases with a DeprecationWarning, few more (at least two) releases with a SyntaxWarning, and finally perhaps a SyntaxError.