Which is a major flaw of the thinking 5 years ago
Unless you scrap new, but displaced stock or there's an exact requirement for them (e.g. the EMR 360s), you end up creating non standard issues elsewhere (e.g. the 707s now at Southeastern, operating alongside Networkers and 376s on the same routes)
Indeed. When the Class 360's were bought to replace the Class 312's, they weren't what FGE actually wanted - FGE wanted more Class 321's (and Eversholt were keen to provide) but Silverlink wouldn't release them and the nomadic 322's weren't enough on their own, so they had no choice but to buy new.
Eversholt eventually (years later) got their wish to consolidate all the 321/322 fleet in one place in East Anglia but sadly, politics and the ridiculous way franchise bidding meant rolling stock cost books get cooked, means that has now resulted in the entire fleet having no home...
So it does have some actual convention beyond a Wikipedia entry?
It certainly seems to have ended up in use across a few areas as a quick search on Google (other search engines are available) shows.
WAML is the commonly used industry abbreviation for the West Anglia Mainline, yes.
Similarly, GEML is the commonly used indusrty abbreviation for the Great Eastern Mainline.
"Whammel" as a way of saying "WAML" is in common use in the industry, yes
(So none of the above are just a Wikipedia thing, no...)
"Gemmel" is not commonly used for GEML in the industry (and I hope it doesn't become so!) - it's normally just called "the GE".