Merging personnel, engineering and supply type things - there's a novel idea that had already been done to a great extent.
DLO = Supply and engineering.
AFPAA = Pay and pensions and will be Casualty reporting, Medal issues and introduction of Joint Personnel Administration to standardize the blunty world across the 3 of us. The people who pay the RAF may be located at Innsworth but they are not part of PTC/PMA.
Manning is a separate issue but cannot really combine unless the 3 services agree on a common way of managing their manpower - as it is the way each manages its other ranks (still the majority of each Service) are different because they are tailored to the Services differing needs. As an example - the Army appear to like their ORs to be young and fit so the opportunity to serve beyond 22 years is limited for soldiers - conversely, the RAF wishes to retain experience for longer and, therefore, has a engagement structure that allows more to stay for longer. Neither is perfect in every respect; but both are tailored for specific needs.