So the ATX/mATX case, where am I with this? Well, I haven't worked on the M5 version lately. Real life stuff, and also feeling a little dissatisfied with the whole thing. Thoughts and things:
W360 doesn't like the "M"-style, just in general. It doesn't blend well with furniture, he says. I kind of agree. He would prefer a more rounded style, something more like what I presented in the OP. I think the M style has it's place, but I also might like the rounded style a little more in general. However, I don't think the rounded style works very well for a windowed/show-off case, like, at all. To the point where I really wouldn't want to offer a window even as an option. That's where I think the M style works much better.
However, a full side window (glass or otherwise) - which seems to be want a lot of people want - may not work well with the M-style. Why? Well, because of how the panels extend past the back of the chassis for easy removal, as they do on the M1. Also, the difference in thickness between the glass and the aluminum sheet is going to cause the window to not sit flush where it meets the front panel. That doesn't make me happy. Alternative is a window-in-panel, but I feel like that's not enough for people anymore. The full side window is the thing now, people want that, plus the RGB lighting and whatever. It's the trend, and quite honestly I feel a little disgusted by it. Not the window or RGB per se - I don't hugely care one way or another - but feeling like I have to follow the trend with my designs, or they won't appeal to people.
So that's the thing. Why am I doing this? I know I'm compelled to work on things that I feel inspired to work on. Things that I actually want for myself. And that changes over time. Like, I don't actually have any need for an ATX/mATX case right now. What would I use it for? I have two ITX-based systems, both in M1s. They do everything I need. But, I've also been looking for a monitor upgrade for a long time - something high-res, high-refresh. If I get something like that, then maybe multi-GPUs might make some sense (though they still seem too finicky - maybe with DX12?). I don't really see myself doing a big custom water loop anytime soon - for my purposes it seems totally unnecessary, and seems like it's really more for looks than anything these days. Air cooling is more than sufficient, and much less hassle in general.
So that leaves the M5 in an uncertain place for me. It's not really what I want, what I personally have use for. And that's most of what drives me to work on things. Making people happy is a good secondary driver, and making money... is what it is - necessary, but thankfully not urgent for me. Either way, those latter two aren't primary drivers for me.
It's not all grim though; like I said, mATX is still something I'm at least a little interested in for future upgrade reasons. And so to that end, I was recently working on a new mATX design - something less ambitious and capable than the M5 concept, without water cooling support, and unlikely to support a window. It's smaller (~20L), air-only, and only supports mATX boards (no ATX). Style is rounded, with less ventilation (solid top), and fewer places for fans. Very purpose-built, with not too many different configurations possible (vs. the broad build flexibility the M1 and M5 have). Some may wonder what the point is, to which I would say, well if you want the same thing I want - a small, good looking, unobtrusive, quiet, low maintenance system - then maybe it's the case for you. If it sounds interesting, I can post some WIP pics.