1.Black smith/ clothing / woodworking: When reaching rank 50, new craft options should appear: Using different mats to craft max level gear (while keeping the texture of that mat) and give small but different bonus depends on what type of material was used to create the item.
For example, Let's call these "post-rank-50" gears : master gears (and always are cap-level)
Steel master gears have the texture of steel gear (of course), and have bonus when applied with health/harden enchant
while ruby master gear has bonus on fire enchant, deals more damage if player dealing fire damage, etc (Just examples)
This provides greater variety of textures of end-game gears (no more red weapons everywhere), and applies some different bonus that ppl need to consider about. Also, on ZOS perspective, while the bonus is minor, min-maxers will go on active and farming the gears with "right material" again, giving more play hour and make ZOS look good on statistic
2.Enchant. In addition to the current 3-runes creation, provide an "essence system" where different mobs drop, obvious ones are flame elementals gives essence that provide more flame damage, frost elements essence provide more frost damage etc. Each glyph can have max of 3 different essence infused in it when creation. This again provides end-game variety, provides more goods in traders, and encourage ZOS to design new mobs.
(Also, players should be given the option to name the master gear with essenced enchant, giving more RPG and artifact feeling, and should be able to attune the gear (if setless) to a corresponding set after completing the hm dungeon or vet trial with the cost of crystals.)
3.Provisioning. I would say add "fresh" bonus but that's probably to troublesome. So let's give each of them unique texture and make them placeable&eatable in houses please

4.Alchemy. Current system is good, we just need more types of ingredients and more different effects.
My ideas focus on the improvement and variety of end-game gears...and especially give them a hard-craft artifact feeling
Don't you feel unfair when skyrim players get loads of artifacts, morrowind players are literally 'artifact sellers", while our good Vestige only touched so few of them?

(and can't keep them...tho indeed make everyone carry same daedra artifact is a dumb idea, glad ZOS didn't do it)
EDIT: Ohh and of course transmog style system and jewel crafting, ppl are gonna bring this up over and over again if I don't mention it)