Although I support adding wastelands, the current plan as shown in the dev diary is a bit rough on the edges, as strategic habitable areas are blocked off.
Southern Nigeria is the more significant of the two, as it's densely populated AND a corridor connecting French West Africa and French Equatorial Africa. While Nigeria would still be available most of the time, it's not guaranteed to be the case, so I suggest keeping it open.
Mauritania is less populated, but it's still strategic: it connects Spanish Morocco and French West Africa, whose owners have a high chance of ending up at war. As such, it should not be magically blocked off. Also, it proved to be viable to support a country on its own, so not really a wasteland either.
c.f.
Southern Nigeria is the more significant of the two, as it's densely populated AND a corridor connecting French West Africa and French Equatorial Africa. While Nigeria would still be available most of the time, it's not guaranteed to be the case, so I suggest keeping it open.
Mauritania is less populated, but it's still strategic: it connects Spanish Morocco and French West Africa, whose owners have a high chance of ending up at war. As such, it should not be magically blocked off. Also, it proved to be viable to support a country on its own, so not really a wasteland either.