You do not need 2 or whatever Gbps backplanes to build
terabit per second networks.
Correct. I've got a terabit network on my desk right now.
Its kind of simple and doesn't scale well... only two ports.
But what can you expect from strands of fiber...
No, gigabit backplanes are not necessary for _routing IP_ at tbps.
It can be done without fancy silicon. I talked that thru with
many people and they agree that there is at least one way to build
a tbps router in a basement. Software is a different matter, though.