Improvements for Season 14: NM Dungeons and Skill Tiers
Admittedly, I have not done everything that the expansion has to offer (currently working towards T9). However, I think there are some easily implementable QoL things that can be done in Season 14 that everyone (or most everyone) would like:
Nightmare Dungeon Aspects (again): One thing that this expansion changed was they removed specific aspects from being rewarded for completing a Nightmare Dungeon. I'm not sure about the logic behind this, but I think it could be implemented again in a way that gives the player some build agency between levels 30-70.
At level 30, Nightmare Dungeons begin rewarding random legendary aspects (at the lowest roll) in a certain category (Offensive, Defensive, Resource, Utility, Mobility). You finish a dungeon, you get loot, and a random legendary aspect (if available). That's it. Players at level 30 and beyond would be able to semi-reliably farm aspects for their builds until they get something useable.
Skill Tiers: The skill tree is boring after level 30, I get that. Most people find the build they want to play by then and just dump points into skills without feeling a sense of character growth. Skill tiers can help fix that.
Every 5 levels in a skill, it gets more powerful. I know it sounds silly, but it could be easily implemented into (virtually) all skills in the game. Even better, the number on the skill that is changing can be color coded like gear quality tiers (skill level 5/10/15/20+ would be blue/yellow/orange/purple).
Skills currently improve incrementally per point to where it is an almost negligible and unnoticeable difference. But every 5 points, you get whatever applies to the skill:
(+) 25/50/75/100% skill damage
(x) 10/20/30/40% damage for a specific tag
+ 1/2/3/4 seconds duration
+ 1/2/3/4 projectiles
Obviously, leave it to the devs to determine what works best for the game, but neither of these changes are too substantial that it couldn't be done by Season 14.