Don’t forget about your current content and longevity
D4 needs to keep expanding on current systems as well as extending the end game.
new inferno horde maps and boons
sigil powder dumps (maybe juice nightmare dungeons and instead of increased rewards, adding another dungeon level)
what happen to the trial system?
fix scaling and bugs so every class has their own specs power level within reason of each other
cellars (maybe a small chance at completion to fall into a hole that opens up a hell run similar to our current root witch thing)
interesting ways to manipulate gear at the end game to make time investment. Corruption, bricking for random rolls, quest chains to add another affix - something that requires VERY rare materials that only drops in t4+
bosses / world bosses / random bosses / nemesis bosses
world events
make legions fun (hell invades at that location and starts pushing outwards to towns and players have to fight them back or lose cities for x amount of time )
more raids
keep expanding helltide (new chests, new events, new super demons, ways to make it harder)
end game activity that isn’t pop / touch this and blast for 30 seconds. Something you work at, like a campaign. Multiple decision paths on the way. Can stop and come back to.
rare currency / runes / something that lets you 1 time change gear (add affixes, make your attacks an element, add an on hit effect, etc), these should be extremely rare and only found in t4
community builders - events that bring us together over common goals. Example world events that provide big boosts to para xp making them worth doing that you stop and head to them when they occur.