Maybe I am misunderstanding you. I have UTP cables on the different locations. No coax though. and neither do I have extra PVR's / STBs. Those all bring extra complexity, costs, power and possible points of failure usage I supposed.
There are many different configurations that you can implement. You could centralise pretty much everything - Core, STB/PVR's, Suround Amps, Zone Amps etc in which case you could use an HDMI Matrix that supports Cat5/6 Baluns (ie it will send HDMI over Cat5/6) in room to send the HDMI picture at full quality to each room. You would then IP control the Matrix to route particular sources to specific rooms and control the TV over IP too (select input, vol +/-, mute etc etc). Your MD's or Media Players can then be centralised and routed through inputs on the Matrix or be located in room. If you locate them in-room then typically you would locate the controlled Amplifier in room too as it makes routing audio to them much easier.
It seems to me that the only reason to have MD's is if you want to use VDR/Myth and access live TV via them and you want to use LMCE on-screen Orbiter UI. If you only want to access recorded TV then you can use SmartTV's or Media Players to access those recordings via upnp (that works for Myth... not sure if can do that with VDR).
This would only need a single Cat5/6 cable to each room/TV location. If you need additional Cat5/6 connections in the room then use a small switch to enable that.
This doesn't add complexity at all.
All the best