First, having a DM-only map layer would be really useful. Consider the archetypal one-page dungeon - it has notes written around the map on traps, enemy numbers, and riddles. Being able to see those, while knowing that my players can’t, would be really useful!
Ideally, I’d like the ability to select grid squares and tie blocks of text to them. There might be a single block with a trap under it, or a room with a save required every n rounds, and it would be useful to tap those blocks and have the text pop up, if that makes sense.