The problem with the North Africa suggestion (which would be awesome and I'd totally get behind it) is that you don't have anything to face OKW late game armour as the brits. Imagine your top tier tank being a Matilda (with a glorious 2 pndr gun) having to fight versus KTs...
Well, Churchill III's did serve in North Africa, so meatshield rush them with AT gun support.
Anyways, i would hope for a standalone Britain vs Italy/Afrika korps to add content that does not involve super tanks and one shotting followed by elite BS. Also, adding another pair of factions into the current 4 would leave absolutely 0 hope for balance because it would be so difficult to do so with so many variables... I would want infantry wars with mass support weapons followed by tons of light vehicles with later medium and minimal heavy tank support - to get a breath of fresh air from the current meta.
Or late war Commonwealth that works and does not destroy everything, yet is cool.
Im hoping for some well done Kursk since that is the next content for anything eastern front related.
Bottom line, i want the next content to be designed WELL. Relic's been designing RTS, and i expect something to be learned from experience.
(And i certainly dont expect Soviets nor Ostheer to be updated because Relic hasnt done any design changes when they were desperately needed, so new content will most likely drown out the problems [or hide them from sight]).