At this stage in the game I would not speak of a GH2 hack in definitive terms.Will this hack contain 25p?
Assuming architecturally GH2 is similar to GH1, it should be reasonable to guess that yes it is possible (if and when the hack does become a reality). Even if GH2 no longer has native 25p sensor mode, the same effect should be achievable by dropping frame rate from native 50p to 25p in AVCHD encoder. Or recording 50p at 1/50 sec shutter and conforming to 25p in post. This way an option for smooth .5x slow-mo is available in post with captured footage.