That's nice you like those boards and risers. Calling the Octominer product a fail is a bit harsh, sure they might not work for your needs but each approach has pros and cons.
I have two riserless rigs (not Octominers but basically the same form factor). I'd recommend nvidia cards with them as they run cooler. Sure you're not going to run 1080ti's (ok hybrids would be awesome but that's going to cost a shitload) but cooling 1060s is no problem with 4 fans extracting heat and 1070s are OK with intake fans and smart heat management around the rigs. I don't miss risers at all on them.
If you are building a bunch of rigs riserless are less hassle too – plug in the cards, ram + ssd, connect fans and you're away.
i agree. i have a riserless 8 card board (not octominers but similar) setup and will never again use risers in a rig. much easier to work on, very stable. cooling is a breeze with 4x140s pushing air at them (open air rig) and its pretty quiet to boot. and depending on slot spacing (it varies per board) cooling 8x1080tis should be doable. mine has 2.5 slot spacing which is a plus, but that means it wont fit in a 4U chassis. but putting 8 monster delta fans in a closed case with a mobo with 2 slot spacing and 8x1080tis could be done (i believe, not seen it done but im sure someone will do it.. love to see that). air flow is king, force enough air through and you can cool most anything. if you can stand the noise of 8x 6000 rpm screamers..
perhaps i will be proven wrong though. whos gonna be the 1st to do it? heh