@libbrit
Well, FWIW I happen to like the Scouse dialect quite a bit, a-thankyuh very much. Really, anything but the Received Pronunciation (and its bastard New World equivalent, the Mid-Atlantic dialect) sounds good to my ears by comparison.
Of course you're right about early American English closely resembling those dialects spoken in Bristol, Canterbury or the lower Midlands (at least, in the coastal parts of America), but there are still traces of Celtic influence on American speech, as well as other immigrants bringing their own additions from across Europe. Those aspects, combined with the relative level of mutual isolation from both sides of the Atlantic (remember, Australia/NZ had a TON of Brit-born immigrants streaming in up until very recently, which helps explain their relative "closeness" to the metropole's dialects), makes for a goodly degree of difference between the two dialect sets. What am I getting at? Well, get rid of that level of mutual non-interaction, and you might at least get a more "Britishy" dialect to stick around in the West that coincides with a more "Americanish" twin set in Britain.