I'm fairly new to MCE myself, being in the process of putting my system together. I have, however been hanging around the forums for a little while and I reckon that you have missed the point of MCE to a certain extent (or I have
MCE has a lot more in common with an Appliance than with a desktop OS. In a working system, you basically have 3 types of computer (I'm ignoring all the Automation stuff for a moment!)
First up, there is the core. This is the server and is the machine hosting the MCE software.
Next, you have the Media Directors. These display the media on a monitor (or TV) and run diskless - they PXE boot from the core.
Finally, you have the Orbiters, which can be web browsers, dedicated devices or applications running on other devices.
Now, let us just take your comments in the light of this...
Ideally the things like follow me should follow each person in the house around: "Kid A" should be able to go from the living room to their room and regardless of what LInux distro they run or phone they have (say iPhone, G1, Palm, Nokia, and so on), Mom go from office to kitchen to living room to bed room... and so on and so on.
The distro has nothing to do with the phone (or vice versa) since for a phone, you'll actually be using either the web orbiter or an embedded app. The real misunderstanding comes, I think, when you say
regardless of what LInux distro they run
The Media Directors are not user PCs, they are (when acting as a media director) dedicated to this function. They don't require a local HDD (although if one is present it can host media files) and they run their OS etc from the core. It is possible to "dual boot" one of these boxes, whereby you tell MCE that the next time the machine booits it should use it's local OS, but then it isn't acting as a Media Director.
I suspect that you are assuming the media appears in a window on the PC, this is not the case.
As a result, your comments on Distro are actually (with all due respect) irrelevant. Yes, you could go to the hassle of getting all to work on SUSE, Slackware RedHat or whatever, but what would you gain? The system is pretty much managed as an appliance through a web interface, so the underlying OS (and therefore distro) is largely hidden anyway.
I can see that if you were wanting to use the machine to play games, or as an Office PC, the distro is important, but as I've already said, you can dual-boot (it isn't actually dual booting in the strictest sense as it always PXE boots, just passes through to the local OS if required).
I hope my rambling clarifies things a bit. Perhaps others will want to comment and I'm sure you will have more to say on the subject - I just wanted to prevent you from embarking on a large piece of work needlessly