Folks have been saying that conduit is the way, and the fiber is the future, and all kinds of things like that for decades so far.

But the simple truth for all those decades is this: When there's already cat-whatever cable in the wall, it generally still works.

Decently-installed conduit (ie, actually-usable conduit) adds a ton of time and expense, which is why it is very seldom used for data circuits in residential structures.

The cable that exists is a lot better than the conduit that doesn't. And copper ethernet is bog-standard like MP3 is: It isn't the best in any technical sense at all, but everything supports it. Universal compatibility is pretty nice.

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So the ongoing cost of copper 10gbe is electricity. Someone else here in the comments says that a copper 10GBe SFP+ module can use ~3 Watts, or that a newer one can use about 1.5 Watts.

We can be generous by using the larger figure of 3 Watts, and 8 devices..

With 4 ports, eight 10-gig endpoints @ 3 Watts each, and $0.19 per kWh [delivered]: That's $3.28 per month, or about $400 per decade.

If we assume 1.5 Watt endpoints, then that number halves.

If we subtract the power consumption of fiber SFP+ modules (or media converters or whatever) to make the number a relative comparison instead of an absolute, then that figure goes down further.

Not so bad, compared to conduit.