Money solves a lot of problems. Fastly already has a geographically diverse set of servers, so I could see them building a feature like this just for Apple (at least initially).
Possibly supporting own relay is cheaper option than just accepting traffic from other companies' relay, but it depends on how they agreed peering to Apple.
Money solves a lot of problems. Fastly already has a geographically diverse set of servers, so I could see them building a feature like this just for Apple (at least initially).