I have been around minature trains since i was 10. now 21 and they are the only trains that i have ever come across with the MU system. i have been to AALS conventions where they have been and there are a lot of people that have not seen it before either and want to get plans to do it for them self. Bear in mind AALS conventions attract people from all around the country.
Although I've never been to an AALS convention, I am aware that people attend from all over. I've been around miniature trains about 16 - 17 years longer than you, although I confess that it hasn't been as regular as your time probably has been. Personally, I don't ever recall seeing any MU operation on any miniature railway (including DVR) but I've seen some locos so fitted (including the 3 you mention). I've read about many more in various magazines, especially overseas, but recall some Australian 5" gauge ones too.
I'm not trying to have a go at you, but try to remember that just because you haven't come across something elsewhere. Doesn't mean it doesn't exist. If it makes you feel better, I've been guilty of this more than once too.
After a few other projects get completed around here, It's my intention to put together the 5" gauge S class parts that have been sitting around my place for far too long. I had two, but sold one. It's a long-term project, but I'd certainly be interested in setting the model up for MU operation. Just a matter of having a compatible standard to follow.