As an occasional contributor: yes please, and as soon as possible!
Most code-formatting issues don’t really bother me much, but I find it quite irritating and annoying to deal with the way that many of libc++'s files have inconsistent indent widths between different parts inside the same file.
Agreed; requiring code changes to be clang-format clean while the existing old code doesn’t even agree on a standard indent-width is not a great situation to be in, since it’ll certainly result in massive changes like you indicate.
Doing the codebase-wide reformatting ASAP would be a great solution to that problem. 