It would be nice to be able to drop in markers that only the GM can see to make notes on that appear on mouseover. That way you can put narrative prompts, ambush reminders, loot descriptions, or DC checks that the GM can have at their fingertips.
“Perception check DC 14 to notice trap door.”
“Enemy kobolds hear players on failed sneak.”
“Lockpick chest DC 12, contains 13 gold, diamond ring, scroll of fireball, singing dancing frog in tophat.”