Buoy-wise, the -60 is already 25%-ish of a P-3, and less than that of a P-8, but a big issue is processing. While the Romeo was a big leap from the legacy -60 in processing, you still need the bodies to manage the data, which now requires more cube room in the airframe (along with more racks on the ship). For what the P-3/P-8 can do with all those buoys is scour an area. 25% of that just isn't super helpful for search and now we're back to localizing/tracking which is what the -60 already is capable of. Plus Romeo will have MAD soon enough.
That said, to maybe refine your overall thesis, what if we moved beyond acoustic sensors, and made that the primary search sensor? It wouldn't take up much room (it would already be a part of the turret) and the speed of FVL would help cover large search areas quickly. MAD is nice when you already know that someone is in the area and you've at least localized him (and gives you a super-warm fuzzy on the attack run), but otherwise isn't the search tool that the Shoes seem to think it is.
I get your overall point is to think bigger than what we've already been using. And naturally that leads to the obvious conclusion. A buoy truck with MAD and optical sensors. I give you, the S-3. You're welcome.