In an interview with Japanese Gemaga Magazine Monster Hunter producer Ryozo Tsujimoto confirmed that the series could soon be switching platforms. As you may know Monster Hunter Freedom 3 on PSP just made waves in Japan as it became Capcom's fastest selling title of all-time.
"The 3DS is releasing, too, so I think the right time to switch [Monster Hunter] to new hardware is coming as well," Tsujimoto told Gemaga.
While it's not a direct indication that the series will switch to 3DS, PSP2 is probably still the safe bet given the longtime relationship between Playstation 2, and then PSP with the series, but who knows? Times are a-changing...