Something I would hope for, is the ability to leave areas of the map blank, for being only dynamically filled with procedural content (or blueprints with randomized decor) if required at runtime.

E.g. house interiors, open plains, etc. That's not making much sense for single player campaigns, but for GM sessions, the ability to patch the world as the session goes should proof rather valuable, as it removes the need to model tons of features forehand, if the players are never going to see them anyway.

This could be expressed in a more generic fashion: Support for deterministic, procedural script plugins, which can be given a free-form area of the map, optionally with a number of fixed features (doors, passages to other areas, bounding box and alike, can be assisted by querying for adjacent features instead). Effectively, "Scripted Blueprints" / "Scripted Brush".

In terms of workflow: Select a region (whereby the engine per default snaps to the edges of a "blank" area, e.g. indoors to the wall, outdoors to the edge of "unpainted" terrain, on painted terrain to the edge of the texture, alternate mode: Snap to "region", whereby the engine tracks regions.), adjust the parameters (including the random seed) and get a live preview of the modifications the script would do to the map. Once you are happy with the results, persist the changes (for alternate selection mode: also persist region information). When in a multiplayer (game) session, distribute changes on persisting.

(Regions can be hierarchically nested.)

A script could perform arbitrary modification to the height map, place all types of assets, paint terrain, auto generate script triggers.

Also the ability to call another script from within a script, to generate sub-features. (e.g.: High level script divides house into floors and rooms, aligning with doors and windows, low level scripts for various room types add the actual interior, lights, rugs etc.)

Effectively, this should allow rather easily to "paint" e.g. unique houses, outdoor features and alike with minimal effort. It also allows modders to share "concepts" instead of just ready baked assets, allowing for mass production of unique features.

I don't expect the folks from Larian to use such a system themselves - they got the resources to hand-place every single pebble in the stock campaign, but for less-than-fulltime map makers, this should reduce the work significantly while avoiding the "cloned" look you would usually get with ready made assets.