I think including it as a searchable option would be useful. You could just have it as a yes/no type thing, whether it allows multi-clienting or not. It'd then be up to the server to state specifics, like if they only disallow it only with multiple clients on one computer, or like some servers I've seen where its a one person per client kind of thing. It is something that generally has a decent effect on a player's decision to stick with a server or not. Some people I've played with absolutely won't play on servers that don't allow them to be their own buffers, and other friends tend to stick with servers that disallow multi-clienting because they find it correlates with communities that do more together.