Hey forums, I tested the GM mode and while it's a neat feature it kinda feels lacking in a lot of quality of life stuff.
I think I can give quite valuable critic and insight because I'm an experienced modder. Mostly for ArmA to be honest here, but it features a similar feeling "GM" mode called "Zeus" where a player is editing a Mission in realtime for the others to enjoy. I'm also a forever master for a 5 man The Dark Eye group for about 6 years now. 
Anyway, here's the list.
- Vignettes
 - Custom transparency and background color for the   textboxes
 - Make it possible to move the text boxes around freely
 - An Option to hide them completely
 
 Vignettes are a great tool to provide visual stimuli and impressions to the players. Sometimes I just use them so my Players can focus on something while I talk and narrate.
 
- Maps
 - Allow us to change the picture of pins and the group icon
 
 I'm quite happy with the overview map so far. They feel great but sometimes the yellow pins are a bit distracting and don't blend in well with the background.
 
- In-Game
 Item Generation
 - Allow us to make custom potions and food
 - Let us change the scaling stat of a weapon/armor category. Ergo Spears that use STR e.t.c.
 - Changeable requirements for generated equipment
 
 Mood
 - GM Volume Slider so I can make sure a player is hearing something and how loud he's hearing something
 - Allow for easier implementation of custom sounds and music
 - "Changing"-Timer between different background musics similar to the lighting and weather timer
 
 Abilities
 - Possibility for custom "skills" by changing damage type, scaling, range e.t.c. of existing spells.
 
 Groups and Movement
 - Allow basic movement commands without pocessing a character ergo strategy-like rightclick commands even for groups of enemies
 
 Stuff
 - Make it possible to design basic Dialogue trees on the fly
 - Give the option to let NPC's "say" something or have conversations similar to the hovering white text above their head in the main campaign.