So for 1.3, I had two major ideas. The first would be to implement the library level, which Wesp restored in his unofficial patch (8.4, I think).
As for the second, one of the most neglected (but potentially awesome) areas of the game is the alley by the Hallowbrook hotel. If you go past the area where you take the elevator into the hotel, there is a large open alley-like space, with a few dumpsters and two warehouse doors (which are scenery and cannot be opened). There is a fence at the end of the alley, blocking the way to the sewer entrance that leads to Brother Kankar. Even back when I played the original, unpatched, unmodded (buggy as Hell) VTMB all those years ago, I felt as if it would be great place, either for a fight or for a secret rendezvous in a quest (since it's very open, but also very secluded). It's a great area that has potential to be part of a quest. Just an idea.