I think $ has the same considerations as *, though not as strongly (* is outright forbidden on Windows). In practice, anything more than ASCII lowercase letters and digits is a Bad Idea. We should stick to lowercase because there are case-folding filesystems like FAT, NTFS, and APFS . (In the last two it is possible to enable case-sensitivity, but most people don't.)
I prefer "auto" to "all", because "auto" suggests creation on the fly (as I assume will be the case) whereas "all" suggests the pre-existence of countably many identifiers.