As far as projected performance in the future goes, Bobik and company would have to be the ones to comment here if you want a solid answer.
I myself would realistically expect between 20% and 40% improvement in framerates before 1.0.0, but that's entirely speculation on my part.
While I haven't heard of any major titles releasing on the Torque3D engine, I am positive that it would take many months at a minimum to port this entire project to something like Unreal Engine 4, if such a task is even possible for a game like this. I do not believe that Bitbox would be able to afford that much payroll right now.
Just saying it how it is.