Realistically it’s probably London. You can fly from Cape Town in 12 hours and they already have the expertise and trust. If it’s an African city Lagos or Johannesburg.

You can say that about Tokyo in the 1980s, but Singapore pulled through.

In Tokyo in the 80s, and probably now, the median financial professional could not work in English, and that’s probably still true now. Tokyo has an enormous and liquid financial market but Japanese is not a regional language, never mind a global one. Paris has a better shot at being the go to place for African finance than Tokyo did of being Asia’s.

One of the best benefits of the EU and Euro was having bond markets in a single currency and reliable set of laws.

Getting just to that level of uniformity in an Africa bloc would be wild and do a lot to solve systemic problems amongst various countries and regimes

You still need a trustworthy legal system and confidence that the local leaders won't swipe your assets. It'll be a while till Africa can compare with NYC/London/Sing on that front.