I think that an Istanbul bid would jeopardize an African bid.
2 risky locations, rio was least ranked as is Istanbul hence risky and Africa would be pretty risky too. Although Africa is due for a games.
I think you'll find Istanbul was ranked above Madrid and just below Tokyo.
It still amazes me that people think Istanbul is risky. Granted it has not held a 2 week multi sport event but few cities have. Over the last few years Istanbul has hosted a very large number of major European and World Sporting events, and has some of the best stadiums in Europe if not the World, for athletics, football and indoor events.
It has held a Champions League Final, A FIBA World Championship and a World Indoor Athletics Championships ... in the last 5 years, all successfully. They have an 75,000 seat Olympic stadium, two football stadiums of 50,000+ one of which has a sliding roof and 4 major indoor arenas of capacity between 12,000 and 22,000 seats. Risk is often associated with the construction of venues and cost overruns .... well Tokyo is riskier because they don't even have their main stadium built yet.
Likewise why is Rio or South Africa risky? Brasil is the 6th largest economy in the world and was hosting a very successful Pan-American Games only 5 years ago. In the last 15 years, South Africa has hosted a Rugby World Cup, a Cricket World Cup, an All African Games and a FIFA World Cup.
For me, cities bidding with bids full of conjecture and artist impressions of future facilities are far more riskier than cities with stadia like the Ataturk Olympic Stadium or the Moses Mabhida Stadium already built and open