Out of all the canidates, I'd say these are the most plausible towards continuing Iwata's legacy and expanding upon it:
Masahiro Sakurai: Similar to Iwata, he was a game developer under HAL Laboratory, president of Sora LTD, and if selected, would be around the same age as Iwata was when appointed president back in 2002, which means fresher ideas in addition to what is already established. He has great overall communication skills with the gamers, but is quite wary of leaks and might lack the drive to run the company.
Genyo Takeda: A veteran at Nintendo, he was the company's first game developer who also pushed the company foward back in the 90's and early 00's. However, he has been opposed to trying out new technology, which would hold back Nintendo even further hardware wise. At the age of 66, he might not want to try innovating outside his comfort zone.
Satoru Shibata: Former president of Nintendo of Australia and current president of Nintendo of Europe, he has had experience outside the japanese fanbase which can mean better communication towards the western branches. He has exceptional mannerisms similar to Iwata's humble and kind ways and has also been in several Nintendo Directs. Overall the most likely groomed canidate, he might not have a strong connection with gamer's tastes and preferences.
Unlikely Others:
Shigeru Miyamoto: A game developing legend, he has admitted that he isn't suitable as head of company, as he is far more engaged in the creative side of management.
Satoshi Tajiri: Creator of one of Nintendo's most reconized franchises, he is currently working under Game Freak as Executive Producer. Might be a stranger to the management side.
Reggie Fils-Aimé: No stranger to the management side of business, he could theoretically bring a western flair to the company. However, it is evident that he does not speak japanese, which is elementary when running a japansese company in the heart of Japan.
