leadarc

http://www.blade-symphony.com/

Closest your getting to JK4.

No one is going to truly help you with porting content to another game engine. And if it gets big enough the owners of the IP will shut it down. If you don't comply they will pursue legal action.

Porting game content to any game with good modding is possible. But full scale content, which you will have to do, takes real work.

Also the fact modders in JK would have to learn a new engines code plus the editors for maps etc and transmit the time it took people do that in JK, years, onto doing another game engine. More time spent editing a game, less time playing it and community interaction.