- A potion called "Veteran's Potion": Give experienced players the opportunity to skip all the meaningless quests (fully unlocked) boosting level to 105 , with maybe even some Arcane Crystals to upgrade gear to Tier 4, increase the XP scaling. Less grind, and noobs still can have their hand held thru norm-hell. Some people might complain this will "shorten ladder season". Maybe so, but it's better than doing the same areas a million times every time you wanna make a new character and try out different builds. XP is the most meaningless metric, turning it into a race to who can get the most XP fastest rewards cookie cutter builds and discourages players from diversifying into something more interesting.
- All trophy bosses should have waypoints or be easily accessible, giving higher QoL for the player for rerunning these areas. Also, trophy RNG should be higher, if not across the board then for certain fights which eat up your time (for example, Yshari Sanctum). The way you can open a portal by disenchanting the sleep charm to Atanna is a huge QoL, it should exist for all of the major bosses that don't have easy access.
- Unlimited Respecs -- Stop punishing the player for experimenting by creating a pointless artificial scarcity. "Build promiscuity" is not a bad thing. We should have plenty of different builds. So what if someone can respec to kill a boss easier? Give them the choice and stop punishing the player by limiting their choices
Chances are, the player will figure out a way to cheese strat a boss anyway. Belladonna potions do not drop frequently enough if you make the unfortunate mistake of respeccing into a terrible build (punishing the player for experimentation).
- More runewords, more sacred unique items, more oskills, skill reworks in general
Progression into endgame requires highly specific itemization and many hours of farming if playing SSF. More options on these fronts would help people branch out into different builds and make progression less of a chore
- More (active) skill variety. Just to use some examples: throwbarb benefited from the rework in terms of replayability, although it still suffers from a limited choice of active skills to choose from. Either you use Stampede, Snake Bite, Overkill as for throwing skills (excluding fortress and guard tower). With Bowzon, you have Wyrmshot, Barrage, and Trinity Arrow. On the list it goes, just about every class suffers from a lack of variety of active skills. What this amounts to is many builds are rewarded for mindlessly spamming the same single skill over and over. This isn't problem unique to Sigma, as we probably are aware many ARPGs are known as cookie clickers for this reason.
- More party buffs or other things which benefit the entire group for group play like farming and grinding XP
- Shared drops
- AI improvements -- most difficulty with end game areas amounts to kiting HP sponge mobs and widdling down their bloated health bars. After a certain amount of repetitions, the novelty of this wears off and it becomes clear there isn't an intelligent/challenging response to the player's behavior (I am excluding bosses here, talking more about general mobs).
Many of these suggestions have been suggested before by others, but I felt like putting everything I could remember into a list. Hopefully it benefits someone.