What I'd like to see is campaign modules - Emer IV, but also a multi-part Thuul, for instance. Plus, northeast Jaiman made right (reboot of Sky Giants). Including technical aspects such as training packages, gear (mundane or magical) and spell lists is OK, but please pretty please, NO new skills !
Second, city books. Lethys, Kaitaine, Izar, even a multi-city book for smaller cities.
Third, organisation books. PoLaD scratched the surface, but there's so much more to say about them. Once again, you can either focus on multicontinental organisations or have a book more focused on a single continent but describing more organisations - Cults of Jaiman, anyone ?
Any of those books can include adventure seeds in the Hook/Line/Sinker form, but I'd rather not have full-blown adventures, especially if the basic hook for them is "you are offered money to tackle one problem" which is something I've *never* used in all my Rolemaster years.
Fourth, or maybe first, a book that twists the arm of Rolemaster magic to make it Shadow World compatible and not the other way round. The current situation requires so much handwaiving and "of course it can be done, just not by player characters" that's it's not sustainable. Have a book that reshape Rolemaster magic *based* on the Shadow World setting and specifics.
I certainly don't need any adventure book, however.