This is a super useful post @dmcmurtrie, and with a quick read through I don’t see anything I’d disagree with, but I’ll go through it in more detail.
We have an internal ticket (RP-975) for our Release Issues Report to compile a list of ‘good’ characters to check against, because our current approach of just flagging as ‘bad’ characters as and when they’re identified leaves us open to repeated surprises. I’ll cross reference your post here.