Hey Steve, welcome to the forum :-)
There's a few reasons why it's under used:
1) My "bad" attitude has driven various people away over the years. I require honesty and a genuine amount of effort. I think that's a fair request, but I'm a kiwi, so my view may be skewed on those items.
2) Technology choice, the platform is a bit dated now, still capable and still a good choice, but not popular. Two other projects have gained similar traction in a fraction of the time with that on their side and really not much else, save maybe a different attitude :-)
3) Hardware is hard. And by that I mean that anyone can install PC software, even from source, on some obscure Linux, it's accessible and easy because of the commodity hardware - well blazed trails. With this, you have to have special hardware which alone is a barrier.
4) Risk. PC software is low risk, controlling your engine with firmware written by some guy on the internet could be deemed high risk, especially if you aren't 100% up to speed with how every aspect of the system and your engine bay works and how best to configure/setup/optimise all of that.
5) XYZ feature that user cannot live without - you may fit this category because factory 60-2 support is not great in FreeEMS at the moment and that's what almost all BMWs use, unless retrofitted with something else. In most cases, XYZ feature is not needed and they could have helped with testing/dev and eventually gained that desired item.
6) Testing turn around. Relying on even the best people for quick testing is a slow cycle process. So I stocked up on cars and promptly ran out of time to implement FreeEMS on all of them. Catch22.
7) Satisfaction. There are two types of DIY tuners: Type A tunes their car well enough, or not even well enough, is happy, and forgets about it forever. Type B continuously tweaks their tune until the day they die. Type A gives feedback, for a few weeks. Type B gets fed up without feature XYZ and replaces with something else.
8) Many people think the project is dead from lack of public progress, it's not. Though it has been slow going... Recent firmware runs cars pretty well, but isn't available to the world, yet, for a variety of reasons. See this vid (and others) for a demo:
https://www.youtube.com/watch?v=e088b5cvF_Y
Probably lots of other reasons, but a fair question none the less. :-)
Now, hardware, not much, only Andy's basic ECU V2 which AFAIK no one has tried, yet. I have one, but have not had a chance, so far. Last I heard he hadn't either, but that was a while back.
The reason for a lack of hardware info is mostly just time/effort related, but also because there have been many many hardware variants, and each person wants something a bit different.
The majority of existing installs are Jaguar variants: A3, 0.4-alpha, 0.6-alpha, 0.7-alpha etc. This is what runs my "hotel" when I get a chance to pour some water in it and do a lap of the block.
May I just say that I really appreciate your taking the time to poke around and read, especially given how needle/hay stack it is. This is the bit in 1 that I called "genuine effort" :-)
Being in Miami (I assume) puts you fairly close to two FreeEMSers (Tampa, Atlanta) with which you could gain a bit of hands on experience in advance, if you want, and they're up for it.