How it all began
When this game was launched, there were 60 Levels to progress through. You could do dungeons, but much of it was spent travelling through the world, doing quests.
Parallel to that, there were professions to choose. You would do so early on and could progress through 300 levels of that at the same time, which was fair enough. You'd average on making 5 skill ranks per character level and life was good.

Then came expansions and pushed the level and skill rank limits higher and higher. Most of the players' time was spent on max level doing endgame content. New characters would try to hurry through the levels, but the path grew longer. Blizzard added alternative leveling options, reduced XP requirements, added heirlooms to cover item progression and extra XP gained. Levelling your professions became a chore, because it slowed your character levelling significantly. People neglected the professions.

The traditional Skill Level system no longer suited a game, where each expansion the skill limit is pushed further and new characters need to go the full path anyway. Recognizing this, Blizzard started to instead push catch-up mechanisms for their professions and opened up expansion content to Skill Rank 1 players. Suddenly, skill ranks were no longer needed.
But they still exist.
Why?

The current focus
With the recognition of the problem, Blizzard has started experimenting. In Draenor, suddenly everybody could start working with Skill 1, though high skill levels were still required for full profession performance. It was still somewhat lacking, but it - in combination with the Garrison's material supplies - at least allowed players to catch up their profession ranks eventually without grinding through legacy content (Who wants to go back to BC? Except to earn that phoenix, that is ...).
The Garrison had several unfortunate effects on the world markets however and heavily impacted the relative worth the gathering professions.
Now in Legion, the lessons learned were applied, providing a profession experience, a profession progression throughout the expansion. While the implementation was not without issues, the experience per se was a great success in my opinion and shows great promise as a way forward.

Profession progression throughout the expansion
This is the key point here.

Changing the progression mode
My proposal is thus:

Remove all Skill Ranks / Requirements
Provide expansion Skill Ranks for legacy content
Assume classic and all expansion content to have a skill rank/level limit of 100
Keep all legacy recipes
Award all players with existing professions Expansion skill ranks equivalent to their current progress in their profession. For example Tailoring Level 345 would translate to Azeroth Tailoring 100 and Outlandish Tailroing 45
Keep a rich mix of progression within an expansion, which can now also utilize a generic skill rank as in olden times (e.g. Azerite Tailoring Level 1-60

Benefits

Consistent Profession progression through all expansion
Fundamentally eliminates catchup issue
Provides new mechanism to scale/extend progression within an expansion (by extending the maximum Expansion skill level, rather than forcing to rely on new materials/recipes)
Allows players to switch their level progression method and still experience Professions while starting to quests in a later expansion's content.

Conclusions
While I do not believe the current system to be hopelessly broken or anything, it is a bit limiting in the tools provided. Implementing this change should offer more flexibility in designing profession content while improving the user's experience with legacy crafting or switching their progression style as they race new characters to max level.

Opinions anybody?

On Profession Progression through Expansions