CDS is earmarked for the Army - Wall or Houghton
Nothing is earmarked as it is the personal choice of the PM and recommended to the Queen.
As the requirement for the next 5 years will be to deliver the CEPP capability, in particular CVF, and replacement Vanguard etc one could see Stanhope as a likely contender. I would say Wall does not even feature, neither does Dalton (RAF told too many untruths in SDSR).