A toolset, on fly event creation is not a must for most DMs. Certainly it is useful, allowing easy on the fly event to be done truly on the fly. However, I would say the ability to fully prepare and create areas is far more valuable.

A few things I would like to see for the GM mode, perhaps they already have been mentioned or confirmed. But I shall throw them in nevertheless!

*The ability to change character names IG, both players and NPCs - A most useful tool
*The ability to speak as an NPC without possessing it - This allows multi tasking during events
*DM spy gear, aka being able to listen as a player speak whilst not being in the same area. - This allows you to run off and do other things whilst they think you are there!
*Full power of player inventories - Adding/removing/Naming/Nerfing/Boosting items IG at will