New engine means new game. Whole game. It´s the same as say it about Half Life for example.
So is it possible? Yes
Is it achievable in modding community? Definitely no
Don´t forget that devs spend lot of months doing new version of mod, for what they have tools. So whole game? Impossible. Freelancer is like Transport Tycoon. It has lot of mods, but still have lot of problems and bugs which can´t be fixed...but it´s legend and we just love it :ylove: