Well BR decided to go for brand new Mark 2 stock in the main for the West Coast electrification, complemented by the AM10 EMUs using Mark 2 style bodies for suburban services out of Euston.
As the AM4s were essentially the LM version of the AM5s and AM8s on the GE, I guess there could have been a use for AM9s on the LM. Perhaps operating Birmingham-Liverpool/Manchester trains.
If an AC version of the 442s had been built, I wonder if InterCity would have been interested in them for West Coast workings from Birmingham to Liverpool/Manchester and Glasgow/Edinburgh? if such a unit had been built, and was designed to be also loco-hauled and heated like the 442s could originally, then they could also have been used on Manchester-Glasgow/Edinburgh services, diesel hauled between Preston and Manchester.
The AM9s were essentially a GE (and a.c.) version of the BEPs/CEPs on the Southern, but with a much tidier front end. No more long distance a.c. EMUs were built by BR (excluding the APT), whereas the Southern went with a more functional design on the BIGs/CIGs/VEPs/REPs/TCs, and kept the Mark 1 design going into the 1970s too!
A long distance version of an AM10 - Mark 2 long distance style coach bodies, compartment seating in First Class and those large curved windscreens and end gangways. Would have looked quite smart I'd imagine.