Is this mad, or what ? Never mind the obvious, what about TCAS for a start?
Not mad, a quite old idea in fact possibly reactivated today due greater automation of flight controls .
The military used this phenomenon already in WW1.
TCAS is not an issue , RAs will only be initiated if tacks converge, not parallel. System only works with RAs coupled to FD which is already the case on the A380/350.
For ATC, also not an issue as they will it will be considered a formation flight ,which means separation is the responsibility of the crews , not ATC..
Smooth air is a prerequisite of course, and how to predict that with accuracy over the oceans is THE question for me.