I think Monster Hunter has a huge chance of going to the PS4, but I don't believe this specific rumor. I am very hesitant to believe anything that fully details the internal strife of a company by someone who is clearly not an employee.
This.
It's not impossible for a Monster Hunter title to appear on PS4, there's one already on there.
The question is the validity of this rumour, so apparently some Dev friend on WoW shared some info just before the Nintendo Direct that had Capcom announce Monster Hunter XX because everyone knew they were going to announce a new Monster Hunter.
Because the name was guessed right, everything else being said has to be taken seriously. How do we know that such Dev is privy to personal details about Sony signing an exclusivity agreement for MH5?
The details suggest this all happened over a long period of time yet the Dev leaks it all just before the announcement of Monster Hunter XX rather than leaking to his friend in the first place long before that announcement.
Other than that, when one leak occurs, we always usually get it from more than one source. After all this time... There hasn't been any other places leaking about Monster Hunter 5, preferably from a reputable source like Eurogamer or Kotaku.
I know someone is going to say that it has to be someone from Japan, then we have WSJ since there is a reporter there who leaked NX details over time and the
PS4 Slim and Pro because he has sources for that.
Not only that, if it's an exclusivity deal with Sony, then it's possible for Monster Hunter 5 to get leaked out of SIE in the US too since that's where they moved to now.