I hope that the Askellon sector will be somehow connected to the old cluster just for the sake of it. I really don't mind about the official 40k timeline, this was never important in my campaigns at all.
They main problem with Calixis was, that it was in the end very disorganized. They started with a nice concept and some short descriptions of the worlds and the powerhouses. With every new book they added content which often referred to certain world or circumstances without having a main source which informs about it. (Like weapons/items which seem the only reference to whole worlds...)
So I would like a detailed description about the main worlds of the sector like the Gazetters which came with some of the adventures. (for example Sinophia in Damned Cities) But for the main worlds/hives in more detail.
There you should be able to find info about the geography & environment, Demography, Government Types, Important NPCs, Imperial presences, note able factions and their relations, note able places, the economy, different Cultures & their tensions, MAPS!
Same also in the other direction, so the sector as a whole. Who are the main powerhouses of the sector? (Great Houses, Alliances, Planetary houses, Dynasties, Corporations, Crime syndicates etc) How do they relate to each other. I would just like to have info about these forms of civil structures. Instead of reproduced page by page information about the Imperium and its structures (including inquisition etc.) which have very little value for the daily life of the common man.
DH 1 content was far too much concerned with the inquisitional branches and obscure mysteries, leaving the social environment where you can set your adventures quite undefined and vague. The setting was very thin and as soon as you started to dig around you could see that it was all just a cardboard backdrop.
I think that the opposite would be better so you can awaken the different cultures and environments where your investigations takes place.
In addition a better planning would be nice. In Calixis we had a lot of conflicting statements. Examples are presences of Sororitas & Astartes or the Navigator houses.
What I expect is a well develop, sophisticated and plausible civil/social background which I can use as setting for my investigative adventures. For good storytelling and rping, you need good world building.