That would have been a perfect solution 15 years ago. Especially given how many other government special purpose aircraft are built on the 214. Now, given development times for the equipment, the MS-21 would be the perfect candidate. And the type needs orders, so it's logical. But that's the real problem, the equipment. Russia needs a modern ASW loadout, a recon suite for maritime patrol, and a weapons bay that can drop hydro-acoustic buoys, sea mines (Russia also needs modern sea mines), AShMs, and depth charges. As far as I can tell all those things are either missing or at best under development but not ready to deploy any time soon.