The bag is actually doing a role more akin to ASTOR / MRA than the original AEW intent - and no bad thing either! However, a significant and important part of the MASC role involves not just AEW, but C2 of offensive force packages, which means better performance than you'll ever get from a pure helo, both in terms of ceiling but more importantly speed and endurance.
Hawkeye can provide the required platform performance, but the mission system performance is reputedly poor and doesn't do the things that the bag does well at the minute.
Sticking the Searchwater on the V22 would go some way towards a compromise between the two extremes, but at what cost? Development, design modification, production of (say) a dozen airframes for the RN and logistic support of same would be far from cheap. Would the current "bag radome" need streamlining to deal with the higher Vmax, and or strengthening the support structure? All allied with an ingenious but fiendishly complex power tx system between the engines that would also have to have generators modded to supply the watts to the mission system.
Nice thought, but unless someone stumps up serious wedge very soon, it ain't going to happen.