I present to the shiel wall a thing for which no one has clamored, but for which a few (especially those missing proficiency bonuses from 5e, or so I’ve been told) might find utility.
Expertise is easy to implement, but it is not like other stats. You put points into it at character creation, and can increase it with loot or milestones. The points in the stat are applied to any attempts or effort rolls related to the PC’s type - so spell casting for wizards and priests, fighting and intimidating for warriors, tracking and sneaking for hunters - you get the idea. The player then gets to add their Expertise score to either the attempt roll, the effort roll, or the crit range. Some DMs for simplicity sake may demand that these choices be set when the points are allocated to the stat. Other DMs may allow the points to float, and be applied as the player sees fit in the moment.
This allows warriors to feel dangerous without being the physically strongest person in the room, is an easy way to reflect professional knowledge without having to be the party brain, or allows more combat oriented folks a better chance of noticing danger before the priest does. It’s a different kind of power outside of the standard stats, and mostly I think changes the fiction of the game more than the mechanics. The important thing to remember is that this stat gets applied only on those actions which the DM determines would be related to a character’s type.
This is still very much an experiment. If you decide to use it like this, or some variation, please let me know how it goes.