The added height, even though slight, raises eyebrows. Here are my best guesses why. Everything here is pure speculation, based on my personal opinion.
Floating keys have been a thing in our community for years. This design was also made mainstream on gaming keyboards. Many enthusiasts here are now adverse to this look.
Custom keyboards have mostly started reverting to a more traditional look with inset keycaps. I’ve seen 3 recent group buys actually proudly stating that their keycaps are properly sunken into the frame (retro60, the doyu custom, and Leandren’s builds). If you browse the comments in other custom board interest checks you’ll often see people asking how far up the keycaps sit. It’s just a sticking point for many. (Not all, but many).
Also, Cheaper (not cheap but not exorbitantly priced) boards often seem to miss the mark, with the keys not “floating” but also not recessed enough... leaving about a 1.15mm gap between the top of the case frame and the bottom of the keycaps. Hence, your sliders make an alps board somewhere in line with cheaper Chinese custom builds.
Old alps boards and cheaper Chinese manufacturing don’t sit right on my mind.
I believe these are some of the lurking factors surrounding the adversity to slightly raised keycaps.
I own all kinds of keyboards. Vintage, handmade, cheap Chinese boards, $500 custom boards. I like all of them for different reasons. I’m not saying that your new design is bad or wrong. I’m just trying to help you understand the logic behind 1.15mm being a factor.