I agree...a lot of the concepts later got absorbed by DAK Africa, and makes such a pavilion redundant unless they wanted a more focused pavilion for a particular country (none of the other pavilions are regional anyways). But no single African country has ever entered into the rumors as far as I've ever heard (other than Morocco obviously).
The Equatorial Africa pavilion would have been completely different from the Africa section of Animal Kingdom.
Here are three sentences from "Africa: The Lost World Showcase Pavilion" at FutureProbe:
Perhaps the centerpiece of the Africa pavilion, though, would have been the show "Africa Rediscovered", hosted by Alex Haley. This fifteen-minute film was designed to teach EPCOT guests that Africa was more than a primitive continent, that it is a country [sic] with a rich history. The show would have highlighted Carthagian general Hannibal as well as the accomplishments of the ancient African kingdom of Kush.
For the rest of the article, see
http://futureprobe.blogspot.com/2008/11/africa-lost-world-showcase-pavilion.html
In contrast, Harambe was designed to represent a scruffy African village near an African wildlife preserve. It's well executed and, yes, it includes some African music and some African-inspired foods.
Again, Animal Kingdom is primarily about animals and World Showcase is primarily about people.
That doesn't mean I still expect to see the Equatorial Africa pavilion built. I'm just trying to make the point that, overall, the Africa section of Animal Kingdom has very little in common with what was planned for the early years of EPCOT Center.
If current Disney management wanted to fund such a pavilion, WDI could tell a great, eye-opening story about the people of Equatorial Africa, their history, their culture, the challenges they're dealing with. It would be something new, not just dusting off the plans they worked on 30 years ago.
It's just highly unlikely ever to happen.