to bring WFA to any other platform is a nightmare imho.
the primary reason is that what makes WFA, WFA is the movement style and physics ingrained into it from baseq3.
I had to jump through some hoops to add the cancer jump mechanic into the physics code of quake4 so that the map style would remain useful.
Another hurdle: porting the maps over from .bsp unelss actual .map files are still available.
another hurdle: the skins in WFA are WFA art. The models are all q3a models. If you port, WFA will lose it's iconic class appearances. Polycount may help with this.
another hurdle: if you move to an engine that has normal mapping, you will have a rough time geting the best model views of our models.
Lastly: Why are you belly aching about the source if you want to port the game to another engine? Do you think I had anything of the original WFA source when I started writing WFR? All I had were every memory of the way WFA played. Every ruleset, every nuance of the character speeds/movement. I recreated the ground grapple sling shot to the tee but changed for the spider man grapple people saw in the WFR alpha because WFR wasn't going to be broken from the start.
You want to make WFA on another engine? get permission to use the name and that's all there is to it. Start writing code now.