On rapid transit, you can only access the underground portion of Leipzig HBF, there should be a complete above ground part of the station that would pave the way for more trains, wether they are ai driven or added to the timetable. And it would be pretty cool to walk there, especially going by foot from underground to above ground
I think that DTG won't add new stations to an existing DLC (in this case Rapid Transit). Maybe this station can be made when they will make another route that starts at Leipzig Hbf.
A lot of people said this at the time, but I assume the time or budget wasn't there at the time (being very early TSW where the core was having to be built out to include German signals/buildings/etc) to model such a massive station and it's rather limited what they could do with Rapid Transit - as they could have added Mainline traffic, even if it was only relatively short distance hops. The main station is very impressive - the underground part rather less so.
Maybe, just maybe, if route mergers ever become a thing Rapid Transit can be merged with a roite that does include the main hall of Leipzig Hbf (perhaps my Riesa - Leipzig suggestion ). However, at the moment route mergers are just an idea, and no work is being done to realise them. Personally I'd love to see the main hall one day, with whatever route it fits on, just because it's so enormous (the biggest in Europe by interior space I believe). Besides it's size it's also really pretty in my opinion.