> The Docker orchestration capabilities are opt-in; they must be activated by the user. Though not opting in may lead to backward compatibility issues down the road.

Whoa, citation needed! Not activating swarm features has the same probability of causing problems as relying on fork() to create a process. Maybe not, but I don't see Docker suddenly forcing everyone into using swarm. It seems unreasonable to even suggest this, and a bit of a scare tactic.