I was already astounded by the price of the gen 3 and 4 backplanes that are out there, so I figured I would disappoint myself by hunting for some gen 5 backplanes. II dont think I found the holy grail, but it is a pretty damn good deal all the same. I found a very curious little backplane on ebay from what appears to be a reputable seller. This listing appears to be for a Supermicro BPN-NVME5-HS119N-S8, and the “NVME5”, following supermicro’s naming scheme, should support drives at gen 5 speeds. They claim, however, that “This Supermicro BPN-NVME5-HS119N-S8 is a versatile component that supports SAS3, SATA3, and NVMe4 interfaces.” The pictures (luckily high quality) show the backplane, and that they forgot an L at the end of the pn. It instead says “BPN-NVME5-HS119N-S8L”. More on the “NVME5” part, the pictures show what appear to be mcio connectors on the rear, which should support gen 5 (as the pn implies). I cannot seem to find the supermicro manual on this, which is odd. All I can find that match it is a wiredzone listing that also states that it is gen 4. Nothing from supermicro on it, however, and it is not on anafra… What an interesting backplane. I dont have the money to buy adapters and cables for this.(… Or do I? Might have to find the money for it…)
If it is truly gen 5, that would be very good value. Slightly related, here’s a bracket that states that this would fit, but they have no pictures and supermicro has nothing mentioning it(?).
I found this on anafra’s site while looking for that backplane by the way, another great offering: the BPN-NVME5-LA26A-S12, which is 12 gen 5 bays for ~240 USD. Here is a server I found that it comes in, a supermicro (829) CSE-829HTS-R1K62LPBP2 chassis. It seems like this could possibly be a drop in replacement in the supermicro 826 2u chassis, but I can’t be sure.
They’re actually rather cheap IMO. I find it funny that the gen 3 u.2 hot swap cages that I was looking at buying are actually more expensive than the gen 5 backplanes. 
if anyone knows where I can get a decent quality cheap pcie x16 to dual mcio 8x card, please let me know. Here is one I found that has redrivers for 275, around 300 after tax and garbage. If I were to actually spend that much money on something like this, though, I would much rather the offering from c payne which has a built in retimer for 267 usd (not including tax and shipping). Might be a fun project to explore. If it fits, then this backplane and an 826 could be the cheapest (and one of the best) options for a gen 5 chassis that currently exists. Video idea, possibly? @wendell