Just to add a couple of points:
You might find the ZWave stuff better developed at this stage, and perhaps cheaper. Hari and others are always working on it, expanding/improving it.
There are a number of devices you can get that are very small footprint and Vesa mountable, so are ideal for MDs. If you get TVs that have a Vesa mount point/bracket this means you can mount the device as a small box at the back of the TV, invisibly.
The WebDT is highly recommended, plus other devices are coming onto the market which could potentially serve this purpose even better. These bring the Orbiter interface onto a portable/mounted device so you do not require the TV Onscreen Orbiter if you so wish. Either way, with HA integrated with LMCE, it can automate many functions for you in conjunction with its other functions, like turning lights out when the house goes to Sleep or Secure modes, dimming lights and lowering blinds when you play media in a room, etc.
Multiroom audio is very achievable, the caveat that ivanp refers to is really just sync'ing the audio between zones. With standard MDs, it is difficult to get a perfect sync, so moving from one zone to another can be noticable if there is much overlap. If that is an issue for you, you can easily setup a multizone amp or multiple amps in a central location and connect several Squeezeboxes to them, then run the cabling to the rooms. The Squeezeboxes maintain a very good sync and LMCE can control them pretty well. Better yet, have the amps actually in the rooms to improve sound quality.
And yes, you can always use matrix devices to switch digital video/audio to different rooms, and control those maxtrix devices through LMCE, the pipe everything over CAT5/6. Personally, though, I think having small, invisible Vesa mount devices behind TVs is the better solution.