I don't think so.
your doubt is based on marketing statistics that based on... well, your assumptions about the market as a whole. a few dots ahead, you point that the enginering improvement is simple, easy, well known and - yes - expensive. Comparatively, it is as expensive as purchasing, from the other side of the globe, a single unit of a very niche non consumer grade motherboard... and we know is not absurd, since we do this all the time, here in this same forum.
As a matter of fact, the very existence of HHHL GPUs is a proof that the market dont care so much about price, since these GPUs sit a bit behind its non-HHHL counterparts, considering raw performance and thermals.
Marketing statistics? Where? My opinion is based on an assessment of production cost, sale price, value and performance.
You're also dismissing some very serious concerns as "simple, easy". Sure, making a PCB with more layers is by itself a simple process. Designing such a PCB with overlapping VRAM traces without causing interference is in no way trivial. Nor do you seem to understand the effect this has on cost - it is significant. An example: look at AM4 ITX boards vs. Intel-platform ITX boards. The cheapest AM4 ITX boards are about 50% more expensive than the cheapest Intel-compatible ones, and this is largely due to AM4's requirement for a thicker PCB. This was also cited by OEMs as the reason for AM4 ITX boards being slow to market. The added cost and complexity is very significant, and will still be so even for a small board like a HHHL GPU. You dismiss this as "just buy a thicker board", which makes it seem like you don't understand the design requirements for a component like this whatsoever. Designing them to comply with signaling specs for sensitive components like RAM is no trivial matter. This exact issue contributes a very large portion of the added cost for HEDT motherboards too, which have the same issue with having to squeeze more RAM traces into a largely similar area as cheaper boards (though they have more space and don't have to resort to exotic solutions like rear-mounting significant components).
Also you IMO seriously underestimate the effect of price and value on sales. Sure, SFF enthusiasts are willing to pay more for more in a small space. But where does this willingness end? A 1050 LP costs and performs roughly the same as a normal 1050. A 1060 squeezed into the same space, or the 1660 I mocked up above will have dramatically less performance than a stock card (no more than 4 memory channels means 33% less memory bandwidth, which means at the very least 20-30% less performance), while costing the same or more (any savings from less VRAM will be eaten by the added board complexity and making a sufficient cooler in the small space). The lack of room for a proper VRM setup would likely impose an artificial power limit/lower boost clocks, or at the very least make overclocking impossible. Would you be willing to pay $230 for a significantly crippled 1660? I'm sure some would, but the vast majority would go for a slightly larger case (still plenty of SFF cases fitting non-LP GPUs) and get the extra 20-30% of performance for the same money.
Tl;dr: IMO you're underestimating the cost, complexity and performance impact of this, while overestimating the willingness for people to pay significant premiums for SFF performance.
