OP I agree with you, it's a great idea imo.
I've been a moderator before on a Discord server with +1000 members, for one of my FOSS projects,
and maintenance against scam / spam bots grew so bad,
that I had to get a team of moderators + an auto moderation bot + wrote an additional moderation bot myself!..
Here is the source to that bot, might be usable for inspiration or just plain usable some other users:
https://github.com/Rikj000/Discord-Auto-Ban
I think it will only be a matter of time before the spam / scam bots catch up to Lemmy,
so it's good to be ahead of the curve with auto-moderation.
However I also partially agree with @dohpaz42, auto-moderation on Reddit is very, uhm, present.
Imo auto moderation should not really be visible to non-offenders.
That would be an anti-virus.. x)
Since it would remove spy-ware from your computer.