In an ideal world:
DRC - my curiosity is too great.
Rwanda - gorillas!!!!! also considered moving there at one point so there's residual desire from that.
Senegal - did a recent road trip with a couple of dudes who'd been and spoke very highly of it.
I don't foresee any of those happening soon, but I'm toying with the idea of journeying from Abidjan to Lagos at some point (and taking in the southern coasts of Ghana, Togo, and Benin along the way) and I think that's got real potential. I tried to get to Madagascar in 2019 but flights and timings didn't work out, so I expect I'll make another attempt somewhere down the line. I've also never been to Egypt or Tunisia but one has to save SOMETHING for when one is too broken down for more intrepid escapades.