is there any chance that the navy envisions multiple rolls
for the same basic airframe, and this decision will get the
cost down per plane for future planes?
You are correct. The current P-3 even now performs far more roles than the basic ASW mission. We do that still, of course, but we also do surface search, reconnaisance (both feet-wet and feet-dry), anti-surface attack, land cruise missile attack, mining, search and rescue, counter-drug ops, and treaty enforcement.
Some of our birds have taken fire recently over Iraq AND Afghanistan, where they provide real-time intel to the boys on the ground.
We patrol the Eastern Med and IO for terr weapons smugglers, plus we still keep an eye or two on the Russians and Chinese.
The new MMA will be able to do ALL of that, as per the Navy's request, plus even more if need be, and it will do it with all-new electronics and weapons.