Ouned knows more about it than me. Maybe you're right and it's just to replace the renderer. I just assumed it would be a lot of work judging by the amount of effort it has taken Xycaleth (who is a graphics programmer) to port it from ioq3 over the years, and it's still not done for Jedi Academy. But the way may be a lot shorter from JA to JK2 than from ioq3 to JA.
It's basically just about API gluing. But OpenJK already has a modular renderer (we don't), so.. still some work.
And you can never know about unexpected stuff coming up while doing it...
In the moment I wouldn't even be interested in porting it as it isn't what I expected it to be. I don't give a fuck about graphical improvements, I want moar efficiency with current stuff. But I guess that would need an overall improvement of the engine itself, so basically a new engine^^