If 1000m is the sweet spot, that's not an issue. It will require TCAS reprogramming to acknowledge the 'Buddy' but read the information people,
This isn't slipstreaming, this is wave surfing and vertical separation is already way less than 1000m in the stack. Two planes 1k apart at the same speed would have plenty of time to take avoiding action, first sign of turbulence lead goes one way, vertically and horizontally and 'surfer' goes the other - simples.
Potential savings are huge, especially as we're trending towards longer, point-to-point scheduling.
Acknowledge the argument that airlines are a (large) net CO2 producer, but at the present time, no other commercially viable solution exists, therefore any scheme to reduce CO2 should be received a little more positively.