Never seen a consumer motherboard with 40Gb Ethernet. Even 10Gb is rare.
One criticism of Thunderbolt is that it already requires a fairly expensive separate controller on the motherboard except for a few Intel chips with built-in TB controllers.
Sending that much data that fast is going to cost more somehow or another.
Right, just thinking about the end-to-end economics. The TB3 add-in card for my HP workstation costs $200 for 2 ports. HP doesn't market a 40g ethernet card but an Intel model costs $400 at retail, also for 2 ports. Then I need either 2 $25 cables for ethernet or 2 $129 cables for TB3. It's the same price either way. Of course, the two setups don't accomplish the same things; they are comparable only in reach and speed.
One criticism of Thunderbolt is that it already requires a fairly expensive separate controller on the motherboard except for a few Intel chips with built-in TB controllers.
Sending that much data that fast is going to cost more somehow or another.