Fiber can solidly hit 10x the price of installation over CAT6a/7, between the more expensive cabling, ethernet conversion on the room terminals (ok, maybe you have one computer with a PCI-E fiber adapter? nothing else does), and the networking switch in a closet/basement (price a switch with more than 4 SFP+/fiber channels. they approach five figures. so, you'll probably have to convert back to ethernet at the source as well).

And the benefit is tenuous. CAT6a/7 can hit 10Gbps, as long as the run length isn't insane. Even the 11th gen Intel NUCs ship with 2.5Gbps ethernet LAN ports, on-board; outfitting your endpoint devices to breach 1Gbps is far cheaper, especially considering most won't ever breach 1Gbps due to hardware limitations (PS5/Xbox? Ikea Tradfri Gateway?).

Even in the "local network upload/download" case; you've got a server, and you want 40Gbps to that server. Building a file server capable of sustained 40Gbps transfer rates is... insane. Its not easy, nor cheap. It requires multiple PCI-E attached NVME drives in RAID-0, on the latest-gen TR/EPYC platform (for their PCI-E lane count, maybe Xeon is good enough nowadays as well). In 2021, this is still in the realm of "something Linus Tech Tips does as a showcase, with all the parts donated by advertisers, and it still sucks to get going because Linux itself becomes the bottleneck". Remember: A Samsung 980 Pro NVME Gen4 ($200/TB) can sustain somewhere around 6Gbps read; you'd need 6-8 of them, in a single RAID-0. And, realistically, you'd want 12-16 of them in RAID 0+1. A server capable of this is easily in the mid-five-figures.

(and, fun fact, even after you build a server capable of this; Windows Explorer literally cannot transfer files that fast. you have to use a third party program.)

If you're a millionaire outfitting your mansion, then sure, maybe fiber makes sense (due to both upfront cost and length of the cable runs, where sustaining 10Gbps on CAT6a/7 is more tenuous). But I think the assertion that Cat6a/7 will be "obsolete" by 2030 is pretty crazy. Yes, technology will continue to get cheaper and more accessible, and I do think we'll see more fiber providers in tier 1 and 2 metro US areas offer wider 2Gbs and 5Gbs connections, but CAT6a/7 is perfectly capable of saturating this. Just ask yourself: Do you really predict that the PlayStation 6, maybe 2028, will have a duplex fiber port on the back, instead of ethernet? Its 2021, and Microsoft's Xbox download servers can't even download game data at gigabit speeds; they rarely breach 250-500Mbps.

Given the niche that fiber lives in, even taking the position that "its just dual-channel light, one up, one down, nothing can travel faster than light, its the perfect future-proof tech" is tenuous. Whos to say that, in the next twenty years, a consumer standard for fiber is developed which runs quadplex (2 up 2 down)? Or simplex (because its "good enough")? Or the connectors are totally different (which would be the easiest to switch because it may not need new cable runs. maybe).

Oh, also: PoE! PoE is freakin fantastic for prosumer setups. and only available on copper. You can run copper to areas around your house where you want security cameras or other smart devices, and not have to worry about also running power.