It's a thought. The reason: When I'm on the road and heading to a greater city with a lot of hosts, I do not know whom I can write with the prospect of success. The option somebody is "available" is an unreliable indicator. Though this option was active, I often got no answer while crossing Canada. Or the answer "unfortunately I'm not at home in this time". But available. OK. Yes I know, people forget simply to care for the right settings. This is human. And I as a potential guest with limited options to go online and check mails while I'm on the road can't ask 5-10 hosts or more at once to find the one.
But I as a host, if I'm available, but unfortunatley not in that days, I could forward the request to other hosts in my town. This could make a mailinglist useful. It's only another click instead of declining. So another host could answer on the request instead of me.
To make it easier to find the members who take part in such a mailingslist on the WS platform can get characterized with a special symbol or another colour.