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In three years, the Swiss banker with Pakistani roots has quickly advanced to the heir apparent should Tidjane Thiam exit. At 42, Khan is far younger than UBS' talent bench, a numbers person, and a capable leader who privately speaks admiringly of UBS (as a former EY consultant, Khan will know both big Swiss banks like few others).

The other name frequently mentioned as a potential successor at UBS is Philippe Hildebrand. The 55-year-old former central banker has effectively reached the olympus of finance as vice-president of Blackrock, but running his hometown bank could mark a career high for him.

Renewed Management Shuffle

Should Weber insist on sticking with his plan for an inside candidate, UBS will have to shuffle its management sooner or later. Keller-Busse was overlooked for a revenue job in the Swiss bank's most recent executive reorganization early this year. 

She currently represents UBS' only female top executive – a far cry from the bank's intention of at least one-third of women in top management. Moving Keller-Busse into an operative role would telegraph to investors that Weber has effectively decided on Ermotti's succession.