It looks like the separate Rulebook is £17 English - which is where I think I will go.
Not sure how they will introduce other gangs either - I have some IG Veterans I built years ago using old Necromunda metal backpacks and guns with plastic bodies - mainly Catachans, which could easily be usable.
The blurb suggests that it is slightly different to the one in the box, as it says something about 'Building a Gang' is different, but it also allows for 3D gaming so if you have any buildings for say Mordheim you could probably utilise those for some form of cityscape.
What I am interested in is how it differs from, or is compatible with, Shadow War