As for The Mapp... I suspect it'll never get a US publication. It seemed to frighten US publishers. They don't seem to understand it.
That seems to point up a significant difference between Europeans and Americans:
A European says: I can't understand this, what's wrong with me? An American says: I can't understand this, what's wrong with him?
I make no suggestion that one side or other is right, but observation over many years leads me to believe it is true.
Interview, quoted in "Words from the Master" in The Annotated Pratchett File