What amazon ebc noticed is that pricing is everything; if you make a decent offer, people will accept it. Since many businesses only need reserved instances for six months or less, you can probably lose very little by renting out your server for that long. When dealing with a large number of servers, I'm not sure how simple this becomes, but I suppose it's the same. The only thing making it less "liquid" is the availability zone. Only those who have a need for servers located in that particular AZ are eligible to purchase the server.