While 10 Gbps networking is getting cheaper, it's still relatively expensive. To connect 3 host cluster you need 3 host ports and 3 switch ports. Starting at $100 per port, you're looking at $600
Compare that 1 Gbps, that's more like $10 per port at $60 total
I figure the reason for 10 Gbps being
so expensive is that if we're talking about 10GBASE-T, it supports cable length of up to 55M. To pull this miracle off it needs to consume a lot of power and that's why these things have this complex high frequency circuitry with massive heat sinks on the NIC cards. But, for most applications that involve high speed interconnects for clusters, 55M is way too long 3M is more than enough.
This is where USB3 comes in. USB3 costs approx $10 per port and the chips are tiny-non-heat-sinkified. And yet, USB3 delivers 10Gbps performance. The only catch of course is 3M max cable length. But I don't want to pay 10x price premium for 10x cable length which I'll never use. The cables used here are commodity USB-C to USB-C cables instead of CAT6 or fibre.
All that's needed now is for switch manufacturers to create hybrid ethernet/USB3 chip (sounds complex, but it's not. All it is is ethernet chip with the transmit/receive part ripped out and hard wired into USB3 circuitry .. all on a single chip to avoid dealing with modulation/demodulation complexities). Slap it into switches and these things will sell like hotcakes. 10Gbps for everyone. For servers and laptops that have USB3 ports ready to go, this can be done with software (a special driver that makes USB3 work like ethernet port)
For inter-operation with legacy networking equipment there can even be a USB3 SFP+ that plugs right into legacy 10Gbps switches that don't have USB ports, but do have SFP (sort of like DAC concept but more cost effective)