I was thinking about using the top case as the plate to hold the switches as well, and it doesn't have to be a metal plate. If I am not mistaken, a Korean guy made a keyboard like this with an acrylic case.
As for alps switches, it is almost impossible to find new ones unless you order them from some Taiwanese company who are still making them. I think a top case for Cherry switches is more practical for now.
I understand that the results of using plate mounted switches without a metal plate is not satisfying.
The problem with acrylic is the thickness, and again it produces a different feel. It's also I think extremely loud. There's one on youtube like this as well and in the mod section. You still need some sort of machinery that will cut it and do so precisely and quickly. I don't think it's a very good solution either.
Most enthusiasts have alps boards, and you can pick up used white alps complicated boards off ebay for less than $50. There's a focus and a blue alps leading edge on ebay right now for $40 that you can harvest switches from if you want. I for one prefer alps complicated and blues over cherry by quite a lot. This is an enthusiast board we're talking about, not a standard production run as far as I'm concerned. This is the thing that will make it unique and have worth and be different from other products out there. It's also possible to offer a harvesting service combined with this board if people get scared by desoldering which I know some are. There are already boards out there that do most of what others are talking about, or can be easily modified by anyone who has spent any time on this forum. I think this keyboards that just have a geekhack key or geekhack brand put on them and are standard runs are missing the point.
I think the point of a geekhack board should be in it's ability to be customized by the buyer and do exactly what the customer wants, be it key layout or switch type.
Most of the people are here on this forum imo because they're looking for something that is extremely rare in the marketplace or doesn't exist. I know that's how I found it and why I'm here. I think a geekhack board should be the thing that fulfills that craving.
I suppose for most people it's a tenkeyless red cherry board? But there are already Filcos like that.
For me it's a hhkb/lowpoly type super mini that actually has usable function/numpad layer programming, large backspace, non iso enter, clicky keys, and doesn't cost $200-300. That's likely never to exist unless we make it.