There is another thread started in February that is trying to explore which dialect of RegEx is supported by Gramps:
And this forum thread was mentioned there. But maybe you can enlist a developer’s help to try using the 3rd Party regex library instead of Python’s native re library?
It would need some performance testing. And verification that it actually expands the case-sensitivity controls for Unicode pattern matching.
The SuperTool add-on might also be an alternative for a deeper level of control than the re library for Python offered.