Meanwhile, compactMap is more concrete and complicated, and uses bothOptional and Array (or Sequence):
[A?] => ((A?) -> B?) -> [B]
These abstractions aren't easy to learn (at least they weren't for me), and a couple design choices Swift has made make them all the more difficult: both automatic optional promotion and our previously overloaded flatMap (soon compactMap) make these functions behave in surprising ways.
I think @stephencelis described the correctness of existing names already, but let me also add that I'm pretty sure map and flatMap fall into term-of-art category of Swift API design.
As for the pitch, I'm against it. Both Optional.map and Optional.flatMap have their uses today and I can't imagine them disappearing.
I stand corrected. Thanks to @stephencelis for the great explanation of the difference between the signatures of the two functions. At this stage of Swift (and this stage of Swift Evolution, as noted by @xwu), it seems that both functions are still important.