It seems like Andrew Gower is still uncertain as to what he wants to do with combat and I think part of is is how to balance thousands of combat levels for PvP, group content, gear balancing etc. I feel there is an opportunity in reducing global combat to 500 levels but reintroducing episodic combat professions to work along side it. I think this could also help a problem the game has right now with the game feeling like rng determines if you can beat an enemy your level by giving combat a little more interaction.

I'll use minefighter as a random example to how this system would work:

Rewards - As you level, you will unlock new techniques to fighting enemies as well as unlocking the ability to use different types of equipment. These would range from being able to reduce the armor of mineral based enemies like stonewurms and metaliths with a pickaxe (based on your pickaxe enchant level) to droping explosives in floor tentacle holes for a fraction of the bomb like how passives work in fractions to deal a static amount of damage based on the level of explosive and stun the tentacle. (of course your character would auto laugh emote if you 1 shot it by using too high level bombs :p)
A couple of ideas for equipment would be a lamp made from refined deathstone by stonemasons and put into a lamp crafted (or repaired from a wraith as a drop) from blacksmiths as an offhand to ward you from necromae damage. This lamp would the be able to be worn anywhere but shine brighter when in the mines giving you more necromae protection.
At a low level, you would be able to hold an explosives sack to save inventory when fighting tentacles. The higher your level, you can unlock a bigger sack.

Experience - Whenever fighting in the mine of Mantuban, you will gain both global xp and minefighter xp as expected and bonus xp for using techniques and equipment unlocked at higher levels.

Milestones - To reinforce the idea that your character is experienced in these different episodes, every 100 levels, you deal a passive 5% additional damage while in that particular episode.
Additionally, at higher levels, you unlock more areas with more deadly enemies but with greater rewards.

Should combat professions make a return? Obviously combat professions would have to be more fleshed out than I can articulate in a forum post and a lot of people hated how they worked originally, but I think the concept has a lot of potential and could help reduce potential bloat whilst not making people feel obligated to gain a crazy amount of combat levels just to keep up with the general player base or give that feeling of "is it too late to start playing?".

As for the levels people have already earned after the rework, use legacy data to give people back the levels they already earned in the previous system and add any extra xp after the rework into global levels.