Thud had features which I would love to see in the game, XP/H, DPS/DPM, Damage calculations for skills.
Blizzard is very strict about not wanting to provide players with extra tools, their in-game Toughness and DPS calculation is often terrible for new players. You see people stack it their DPS to 2m, but they do less than 1/5th the damage of someone knowing to stack particular items and have a sheet dps of 500k.
Bliz should look into what GGG (Devs of Path of Exile), adding features of the popular HUD into their game because they saw players WANTED them. Yes, within reason they shouldn't add things like Map hacks or tools that track mods locations on the map. But compromise, look at what things would benefit the game.
And before anyone attempts to accuse me, I don't use THUD. I can just acknowledge that various features would be a nice QoL update.