Of course I realize that players want new rewards every new content addition. I also realize that players love frequent content addition. Finally I grudgingly accept that video game designers must cater to bad players too who want to progress their characters despite being horrible.
I finally cooked something that solves the reward reset problem without taking away any of the three reasons it was created. The idea is every content rewards one type of gear. The player would start with leveling to max and during leveling he gets ilvl 100 items in every slot.
The first “content” (dailies, factions, dungeons, raid) and get helmets. Only helmets. The dailies get him reputation with the faction that sells ilvl 105 helmet on friendly, 110 on honored, 115 on revered and 120 on exalted. The “heroic” dungeon gives 110, the mythic 120, the mythic+ up to 125. The LFR raid gives 105, the normal gives 115, the heroic gives 125, the mythic raid gives 130.
The second content does the exact same thing with necklaces, except the content is tuned a bit harder, because it assumes that the player has the appropriate level helmet. So the heroic dungeons are tuned to 110 helmet wearers while mythic raids are tuned to 130 helmet wearers.
The third content does the same for shoulder items, tuned to players both having the proper helmet and necklace.
The best players would finish the content in every turn, picking up a mythic item to every slot. The lesser players on the other hand would jump around between tiers. I mean a baddy can’t get better helmet than the ilvl 120 by farming exalted with the faction. He can’t do heroic raids or mythic+ dungeons since he sucks. But after he also got the ilvl 120 necklace, he can go back and do the first mythic+ dungeons for his helm, since those are tuned for players with a 120 helm only and not 120 helm + necklace.
This way practically all content is relevant, give rewards and have tasks to do for all players. But more importantly, everyone would have to do the same content for the rewards, the ilvl 130 helmet only comes from first content mythic raid and one has to go there for it. Sure the best players got it with ilvl 102 characters and some player would do it with ilvl 120, but still he had to do it.
During one expansion (about 2 years) all slots would be filled. Of course if there aren’t enough content patches (1 in 3 months mean 8 per expansion), the scheme can be changed to 2 slots per content.
What will happen with the new expansion? Only partial reset. The quests of leveling would give ilvl 115 into every slot and the first content would be about helms, giving 15 ilvl above the old helms. So old mythic raid helm is still as good as new normal raid helm. So new players could start to catch up, but old good players would have a head start, rewarding them for past playing.