I realise the devil is in the detail but a fleet of P8 Poseidon’s - with some fitted for future AAS Radar (if we’re permitted to buy it) and E7 Wedgetails would give the RAF;
Airframe commonality (relatively speaking).
The ability to draw upon previous CFM-56 expertise from E3D and RJ.
A not unreasonable possibility of pooling pilots, simulators etc.
Therefore you could have in the near-mid term a Nimrod and E3D replacement with a viable option to replace Sentinel. Though I admit there would be a degree of ‘Jack of All Trades’, surely it would be more efficient - especially if we are potentially hurting for future Aircrew Numbers and money etc?