The main problem with multihoming is syncing the servers. Static sites are trivial to multihome, but how would you do it with this forum, for example? People would post to the same thread on different servers, so when they returned to the thread later, they would see posts before theirs that didn't exist before. Someone deletes his post on one server and another person replies to that post (quoting it) on the other server. How do you handle that? It would be chaos. One solution is to use 3 servers. Server A and Server B run SMF. Server C runs the database. A and B are connected to C as a remote database hidden service. This would add a few seconds latency to each page load, but that's a trade off that could be worth it in some situations, like if you're using sketchy Russian hosting providers with frequent power failures and you need multi-homing. A and B also store local copies of the database which they don't normally use, but if C goes offline, then B shuts down and everyone uses A until C comes back up. People on B would still experience brief downtime that might be indistinguishable from routine Tor network fuck ups. The market would be easier to multihome. The main problem I see is when listings get low on stock, people on different severs may buy the last sample. This could be handled by displaying a message when the listing goes below 5 items, which says that you have tentatively purchased the item, and it may or may not complete within an hour (or however often the servers sync), and the buyer will be notified of the result. Or it could be handled with 3 servers as above.