Python should still work reliably even if the temp directory is on a case-insensitive filesystem. Since that isn't an easy thing to determine, -1 on restoring the uppercase characters to the filenames.

As for it not being fixed previously, it's a rare bug that only affects case-insensitive filesystems. Just because other groups have decided not to care about it (typically due to a heavy bias towards case-sensitive POSIX filesystems), that is no reason for us to ignore it once we're aware of it.

If we really wanted to increase the entropy, better to increase the number of random characters included in the name to 7 or 8 (with each additional character increasing the pool size by a factor of 37). After all, why perpetuate an arbitrary restriction that is due primarily to the difficulty of constructing nice string manipulation interfaces in C?