I'm all for that but suspect it can be compressed further and limiting to "follows of follows" or "follows of follows of follows" would spare you the bulk of reports as these are unconnected accounts.

Find my follows. Find their follows. Find their follows. Find all the rest **by** and **about these pubkeys**. A report authored outside of that group is irrelevant. Pubkeys outside are "unknown". Reports by the in-group about them add little signal. A new spammer is "unknown" while an old spammer is known to be blocked. Hopefully we get heuristics about older accounts outside the group somehow but to give a new account some credit will only result in spam getting sent with only new accounts.