What sort of WAN/MAN links would have the bandwidth to do HDMI video ? I seriously don't see this being used over a WAN/MAN.
If you are talking about inside a large building, such as an airport, why is there a need to route between the different Comm Closets ? You can keep everything on the same VLAN, even in those situations. The only reason to route on a LAN would be to connect multiple subnets, and since all of these HDMI devices would be on a single subnet, there is no need to route. In fact, since it is running traffic that you never need visibility of on your servers or workstations, you don't even need to route between these devices and your network. It is a totally segregated VLAN. In large buildings such as an airport or office building, everything is designed with Layer3 switching until you get to your WAN link anyway, so there is nothing preventing a design that allows you to push the HDMI VLAN to every corner of the building. I am just having a very difficult time trying to figure any solution that would require this HDMI network to traverse a WAN/MAN link, and who would pay for such a beast, since they would need a HUGE pipe leaving their building.
Even in the case of a campus sized layout, it is easier to run HDMI over fiber between buildings, then HDMI over IP systems inside each building, since in a campus network, you have the ability to run your own fiber lines from building to building.