There are lots of things that behave differently depending on the currently set start method: Lock(), Semaphore(), Queue(), Value(), ...  It is not just when creating a Process or Pool that you need to know the start method.

Passing a context or start_method argument to all of these constructors would be very awkward, which is why I think it is better to treat the context as an object with methods Process(), Pool(), Lock(), Semaphore(), etc.

Unfortunately, I do not have time to work on this just now...