Seems by the best option, IMHO. No such pesky thing as real life to interfere in the history, and the added flexibility is a substancial advantage. I for one felt the original planning was a bit too constricted, especially given the scope of the first three CM games. More room to expansion is always a good thing!
As for history and background, they are indeed easy to create. Let's say, for example, that a important ally of the USA in the middle east is facing a civil war, backed up by not so friendly nations of the middle east that are trying to replace the government of this country. USA is called to save the day, and face the rebels and maybe elite forces from those other countries that are fomenting the rebellion (pretty much the same thing originally planned for Syria forces, I think). Plenty of room for other countries to get into the fray, which would justify all kind of equipment, european, chinese, russian, etc.
Just my 2 centavos.