w360 mentioned there might be cards going 3.5 slots on the next generation. at its current state, only watercooling would be feasible, thus further increasing its niche
if the orthrus goes 4 slot wide, there's probably not enough PCIe lanes to justify the lower deck (maybe a custom disk backplane could fill the space that wide), and it'll be twice as thick
speaking of which, if one wants a small board with PCIe lanes, they'd have to turn to server boards, and those are probably adopted too few outside the enterprise space to be considered above speciality. it's the chaotic end of sparing no expense for the most compact and performant system
to re-iterate, nvidia and AMD is moving away from multi-GPU for consumers. it's increasingly likely that those who want two xx90-class cards would fancy a larger case, or would be alone in trying to cram that into a shoebox (edit: and that's before considering the power draw. 1kw power supplies just barely started becoming a thing in SFX-L)
it breaks a few hearts to say this, but there might not be much volume for engineering something new for the past when it comes to PC hardware
