Do we even want a new JJ game? Seriously now, excluding the obvious fact that the community is small (not that this is necessarily a bad thing), a new game would probably be different from what JJ2 was. The level editor will probably be more limited (and definitely harder to use, especially considering the high probability of the game being 3D).

Overall, the game would lack the open-ended aspect its prequel has, so it would really need to be a hit to actually attract long-term metagame players.