I think there are two major possibilities:
-
A second invasion of Ubersreik
In this case the Skaven and Northlanders attack the city.
Old maps get reused but overhauled to fit the narrative and gameplay.
major DLC -
The original invasion
Only rats, no Northlanders. Now with shields, monks, flamers and stormfiends!
AI director gets adjusted to fit the old maps.
fast and not too much work