It's all good
I am with you for sure. I feel the same way, I always have a problem paying more and getting less. My observations is that people doing the BRIX and NUC and ITX builds are certain types of people in certain circumstances that are looking for something simple, small and a decent value.
They are not concerned with squeezing every last ounce of performance (MadVR type stuff) and just want a nice simple experience. For those people the NUC and BRIX is a great choice, but crowdsourcing an ITX to compete with such things is going to cost more and probably not be as good as alternatives. So- it's a pointless attempt. A crowd sourced project would likely need to cost some decent money just for a case ($100+)
At that price point your talking about a different person- with different needs. A true enthusiast would spend a couple hundred on a case, but not everyone would. At the enthusiast level my observation is people wants specific things, and they are looking for a bit more. They tend to have a bigger system (like a theater or an AV rack) and for which ITX is a poor choice.
I would be mildy interested in an enthusiast level case that is MATX or ATX component style, could accept a video card, and had read outs for CPU TEMP, case temp, fan speeds etc..
My theater project is starting and I plan to have a thermometer LCD readout on the top that lists the AV closet temps internally, and the temps of my server, HTPC and PC. But my project is going to require lots of custom wires and only would apply to a dedicated rack of some type- certainly not the same category as a cute NUC sitting on your cablebox in the living room.
The cost and point of a crowdsourced DIY HTPC case goes beyond what people want, or need, or are willing to pay. I think the need and desire for ITX style is misunderstood, those same folks that want it won't want to pay for it. Not when there is plenty of cheap MFG options out there. Besides building in ITX is no fun..