What's the point of Cat8 if I can't find 40G RJ45 transceivers?

Cat8 was developed alongside 25GBASE-T and 40GBASE-T as a short-reach data center cabling option. The cable standard doesn't guarantee that affordable, widely available transceivers will follow.

Those copper Ethernet options saw little adoption. Fiber and direct attach copper cables were already attractive for high-speed data center links, while Cat8's short reach made it a poor fit for typical office runs. That's why a cable can support the standard on paper without being a practical way to build a 40G network.

For a new install, I'd normally look at Cat6A for 10G Ethernet rather than pay extra for Cat8 on the hope that 40G RJ45 takes off. Check the required distance and the equipment at both ends before choosing cable.

For a short, fast link between compatible devices, a direct attach copper cable is worth considering. For longer runs or other high-speed links, look at fiber and compatible optics. Neither choice depends on finding a 40GBASE-T module.

There is a future-proofing argument for installing cable ahead of the equipment, but it only works if the equipment eventually becomes practical. Cat6A had a clearer path to 10G than Cat8 seems to have to widespread 40G RJ45. I'd be cautious about spending extra purely for that possibility.

Heat and power are part of the problem too. High-speed Ethernet over twisted pair needs a lot of signal processing, and the ports can run hot. Fiber optics and direct attach cables can be more attractive on power as well as availability, though the exact draw depends on the hardware.

RJ45 cabling still has useful advantages outside high-speed data center links. It can carry power to devices such as access points, and field termination is convenient. But those benefits aren't a reason by themselves to buy Cat8. You can get them with other Ethernet cabling too.