mechmouse: I'd love to have seen a continuation
SMG in her 40's trying to hold a Job, look after a Daughter (possibly a slayer) as a single mum and Slayer/Leader duties.
Or a Spin off in the same universe
Hellmouth 101
As stated there are plenty of Hellmouths, it was just Sunnydale was on THE hellmouth. Close that the others become more active.
600+ hellmouths across the globe this is Hellmouth number 101. New cast but with cameos from the originals. Also with every potential becoming a Slayer the balance of dark and light gets screwed up. We get Dark slayers, void of empathy (makes Hope look sane) and also Vampires that don't loose their soul when turned. Muddy up the good/bad narrative.
If it is a reboot, keep the original past, just have a new slayer named Buffy in honour of the original.
From what I can tell there is none of the original cast involved. i do like those ideas you present.