I don't know how I could have possibly over looked this but the solution to alt spam as been right in front of our eyes the whole time!
There happens to be another java game called Minecraft, and there happens to be a griefing tool for said game called 'pwnage'. Now, what pwnage does is you feed it an alt list (most 'good' griefing teams have at least 900 or so) and it will connect to a server as many alts as will fit, as soon as a server slot opens up it puts in another. The tool lets you sort of remote control them all.
Sound familiar?
Weeeeelll there just so happens to be a server side direct counter to pwnage called 'nopwnage' which detects pwnage and rapidly bans not only the accounts, but the proxies as well. So the griefer very quickly depletes his supply of alts and proxies.
"But Servant_Girl, that can't apply to HnH because the alts leave hearth fires and are free and therefor infinite"
True the greifer cannot 'run out' of accounts but I feel like a server sided counter could work in the same way! It could detect when new accounts are rapidly all using the same HS or all using a HS to the same immediate area! No set 'limit' or number...just it detects them being created at a speed faster than a single person would be able to do.
The counter program would kill, and delete the alts from the database. If they're not banned in the creation room then they would all be banned just as they appear on the surface! Character file deleted, HF gone!
No gameplay change, no account restrictions, a sever side fail safe that directly attacks the problem and only the problem.
I am Servant_Girl, at your service.