Chip Brantley, whose pluot book I recently reviewed, has also recently penned an article on the distinction (or lack there of) between plumcots and pluots.
The Whole Truth About Pluots Versus Plumcots (Slate)
As I have mentioned before, I myself definitely favor "plumcot". I'm bothered by the idea of something trademarked becoming a generic term for something for which there is no real non-trademarked term, which would be the case if one insisted that plumcots are solely 50-50 plum-apricot hybrids (well, I suppose there's always "interspecific plum", but come on...). It restricts discussion and trade by people who don't hold the trademark, and it dilutes the trademark, so pretty much no one wins.
On a semi-related note, does anybody know the exact species make up of the "cherums" I've been seeing in the store? They've only come in big packages, so I haven't yet bought one, but they look pretty heavy on the plum side of things. I'd be stunned if some one could get any fertility of consequence in a cherry x plum hybrid without a bunch of backcrosses to one side or the other, but I'd be curious just which species they're working with. I'd wondered if maybe it was really a hybrid with the cherry-plum, Prunus cerasifera, but if you believe what little I've found online, it sounds like it involves actual cherries...