Another thing I'll mention that just doesn't really sit well with me.
Just how tied up in FF you are.
Talking about the source13 and OB ports.
I understand that porting FF to a newer engine, could help with porting the physics and programming. (although I'm not sure really how much, in terms of a work:reward ratio) But like I said before, I really think for a new iteration of fortress game play to take off, it'll require a full rebranding. That may sound a little drastic, FF is small enough that, a newer, properly made version may not have that much of a negative connotation to it. How ever I'm confident a more meta rebranding is called for. The class names in particular. You can not have a combat focused class and name him the medic. You can not have a movement based class and let people think he's competent at combat.
By the time you have a quality Fortress game, what is left from FF other than physics code? So is a port really worth it?
And if a ports not worth while, is source/2 really the best way to go? I think everything about steam is great, with work shop and all that integration, but you can set up all that with any game can't you?
That being said, Phish has had bhop running in UE4 for quite a while now: