Oh boy, this again.
I don't think a Monster Hunter exclusive would even be a worthwhile thing for Sony to pursue. The PS4 is doing fine in Japan, about as well as the PS3 did. It's not going to fly to PSP/3DS levels because of Monster Hunter. I think Sony is content with the PS4's performance in Japan and is more interested in competing in the much larger Western markets, where Mon Hun pulls no weight.
Monster Hunter is still one of the strongest franchises in Japan, but I think it's lost its enormous influence. The game has spawned its own sub-genre with multiple competitors. It may have lost some of its fans to God Eater, etc.
Most notably, Japan is in the process of shrinking from a 4-platform ecosystem to merely 2. Once upon a time there was a handheld generation exceeding 50 million console sales alongside a home console gen of more than 20 million. Those days are far behind us. Now there is one home console and one hybrid platform, and two slowly-but-surely retiring handhelds.
