Take your existing D4 ‘things’ like Sigils. Make them upgradable. Enhance player gameplay or make the game harder or more survivable etc etc as the player wants. For example:
The powder of ten sigils adds a new boon and bane to a Sigil. Make the boon a choice of xp or extra gold or speed or ten whatevers to choose from and then the bane is random. Monsters do extra dam or respawn one time.
But allow for up to ten upgrades. So they can turn Nightmare Dungeons into a Hellraiser Dungeon at the pace of the player. And make each level 1.2x harder than the previous level.
Elixirs and incense now craftable. Combine two elements of whatever. (Like TES Morrowind enchant system). Speed and Fire Res. Or Armour and crit.
More and more variety of incense and elixirs. Make the list of options huge.
Allow for two or three tiers of stackable elixirs like incense and all craftable too.
Make the rune chance to upgrade be 100% and just drop 80% less of them. Instead of tons of useless unused runes. “85% chance to be stupid, 15% chance to maybe be better” is infuriating design.
And make more. Like 50 more. That are wild and creative.
Or give runes a better second functionality.
RNG shouldn’t be in e v e r y t h i n g. Give the player 25% control back. Little character enhancements or tweaking difficulty on dungeons or hordes or Kurast or new S7 systems.
Give me my construct back. WHY would you take that away. Utter madness. That was a lot of fun. And could easily be a permanent thing. Easily.
Heck let us discover manuals that allow for redesign/reskinning the thing. Add new powers on the DL so people get an ‘omfg’ moment. You know. FUN.
Make uniques do stuff like the skill tweaks in D3. Meteor is now poison. Or Frenzy now counts as Double Swing. Go nuts dev team. Add 4 new uniques per class every season. And let them all be accessible in perpetuity.
Stop being so scared to get crazy. This game has been on the cusp of brilliance for soooo long. Just dive in ftlog.