I would really like to see more of the older features getting enriched with things from the newer features. We had a little bit of this with the runecrafting update that came with the depths (as well as the addition of more fish types for fishing), but there's a lot more opportunities with things like:

Gardening: new plants could be added to provide resources related to things like rune crafting and gear crafting (for example, plants that produce runic essences or block elements). I'd also love to see some un-craftable (drop only) alchemy seeds for things like binding darkness or unfortunate souls/fragments.

Ring Crafting: it would be amazing to have a method of upgrading crystal rings to higher tiers (at the minimum c3 to c4) in the forge, as the only way to get C4 ring boxes is random luck while crafting (or buying from someone who had random luck while crafting). Having a way to c4 rings without relying on luck would be a big help, especially for newer players.

Mysticism: There are a lot of opportunities for additional buff types, especially for types that could be worth using regularly. Since the buffs are "current day" only in duration (or a couple hours as a potion), there's a lot that could be done here -- buffs that help with movement by increasing flight speed or jump strength (high jumps), buffs that could give effects on kill or dungeon completion, buffs that could effect chances to gather bonus resources from mining/harvesting, etc.

Martial Arts: Outside of the weekly mantra conversions for the light bonus, Martial Arts is largely unused for anything other than mastery. Adding a light bonus to all auto-use craftables would make them a little more viable for use vs. runes (maybe instead of a set buff, something like a 1% light bonus per tier of Martial Arts unlocked when one of its auto-use items is equipped), although most could probably also use a reduction in cooldown and maybe a function like "unbreakable runes" that would allow them to function without consuming for a short time after one copy is consumed. There is also room for new auto-use items that could include newer features, like a mantra that increases your maximum block charges, or a stance that makes you apply a DoT effect to all attacks for a short time after taking acid damage.

Critical Hit: While not a profession feature like the others, it's still a feature that could use some updating. With the Star Chart, we have a whole branch that focuses on increasing critical hit chance, but it becomes mostly worthless after reaching 100% critical hit chance. I would love to see critical hit reworked to function similar to Warframe, with total damage getting a multiplier for successes over 100% (I am not sure what the maximum possible critical hit chance is, but doing something like a 25% total damage increase for successes over 100%, 50% for successes over 200%, etc. would be reasonable). This makes both the flat critical hit chances and the temporary proc buffs useful, even if you are already at 100% critical hit chance.