An MPA has always been a multi mission aircraft. It's primary role is and remains ASW and there is no other tool in the toolbox that can do what an MPA does in this area. It's secondary role is ASuW, with the ability to provide sensor to shooter capability in rapid time. The Falklands war proved just how deadly a long range air to surface anti ship missile can be. Thirdly is an overland ISR capability which was conducted for many years over both AFG and Iraq. LRSAR is really a bonus capability and most certainly not the primary role. However, a certain oil rig event in the 80's (Piper A), showed just how valuabLe an MPA was as a Scene of Action Commander. Similarly, a Rod was first on the scene for the Air India disaster in 1985 where the crew did visually identify wreckage in the water and confirm the location of the incident. Richard Branson could also tell you how much he valued the services of a Nimrod during a couple of his adventures.
So , 4 clearly defined capabilities that are still required with the potential to expand into Sentinel and RJ territory. Oh, and had the MRA4, made it into service, it had the ability to carry 6 Storm Shadow with a 14 hour loiter abilty. That would have been nice off Libya don't you think?