I think his point is an issue of time and wear. We saw this with FF where time was the brands largest enemy in Japan as it spent near a decade faffing about with Lightning and it's audience simply atrophied with time and being unengaged. (Contrast with the extensive maintenance for DQ on both it's platforms.)
In that time, World has to maintain engagement in the face of a bad port doing nothing on portables. World will sell a fraction of 4/X in Japan, so it will fail at this maintenance spectacularly barring some major turn-around. And even more, the maintenance isn't even based on MH's strength in Japan. It has to make this up by breaking major ground outside of Japan.
Then the next question is when... When is the next Portable? 2019? Where's your audience going to be by then? Will it even still be interested? Did it transition out of the market while younger audiences "grew" into Splatoon or other franchises rather than Monster Hunter? This is his point. There's nothing for the portable audience to consume, it will fade or move on. They're not being engaged and if taken for granted they'll eventually simply be gone.
There's no foreseeable maintenance planned due to Capcom's general poor planning leading into the Switch.
