> They can just plug in their ethernet cables like normal, except they'd also have the option to switch to something better in the long run.

I don't think many will exercise that option, and it adds complexity and costs that most people won't need. It would be useful for some, so it would make sense to make some boards with sfp+ rather than an integrated transceiver, but not as the default.

If you want 10G sfp+, Intel x520 cards are cheap on ebay.

The cards might be cheap but they tend to be very hot and wasteful in terms of power. Only the newer more expensive modules finally support PCIe ASPM properly. Lack of it might actually also increase overall system power consumption due to certain sleep states becoming inaccessible.