Speaking of filling gaps, I really hope they fix the uninteresting mess that is the current set of transitions within the African continent. Seriously — what do Aksum, Songhai, and Buganda have in common besides 'oh, they’re from the same continent'?
It would be fantastic if they released a civ pack specifically aimed at fixing this, and here’s what I’d suggest:
Kilwa (exploration): serves as a bridge between Aksum and Buganda. Not perfect, but definitely works better than Songhai.
Ethiopia (modern): an alternative transition from Kilwa and a direct connection of Aksum.
Ghana (antiquity): a proper predecessor to Songhai.
Sokoto (modern): a fitting successor to Songhai.
That way, we’d have two African historical paths that actually make sense:
Ghana > Songhai > Sokoto
Aksum > Kilwa > Buganda, Ethiopia
They should also add leaders relevant to those paths. I’d suggest Mansa Musa and an Ethiopian leader.
Somalia could also come later as an alternative to Kilwa, offering a stronger connection to Ethiopia.
Finally, they could expand into other parts of Africa in the future — for instance, the southern region — with a historical path like:
Bantu > Mutapa > Zulu
And if Southeast and South Asia are getting so many wonders, it would be great if Africa received some love in that area too, with a few disassociated wonders like: the Great Sphinx of Giza, the Great Mosque of Djenné, and the Church of Saint George of Lalibela.
Not taking into account a Caribbean leader that could also lead into Mexico or Gran Colombia due to geographical proximity (less of a fan for this btw.)
Regarding a Caribbean leader, I’d suggest Anacaona. She wouldn’t be linked to any other civ except the Taíno, though. For a modern Caribbean civ, I’d go with Haiti.
Unfortunately, Haiti suffers from having many of its thematic niches already filled:
Revolutionary civ: Mexico
Revolutionary Latin leader: Simón Bolívar
Considering the possibility that Mapuche could end up in Modern, I wonder if Inca>Mapuche would work?
It could still work, but thematically they fit better in the Exploration Age — they even interacted with the Inca, for that matter.