I think World of Warcraft could benefit from adding level-specific requirements to certain achievements that give unique rewards. This would encourage players to make alts and play through older expansions at the right level instead of just blasting through with a max-level character.
Why this would be good for the game:
Keeps Old Expansions Relevant – Players would engage with dungeons, quests, and raids (at the level they were meant for), making them fun again.
Boosts the In-Game Economy – Expansion-specific potions, gems, enchants, and gear would become valuable again.
Encourages More Alts – Players would have a reason to level and keep characters in different level brackets instead of always rushing to max level.
Brings Back a Sense of Progression – Instead of skipping over entire expansions, players would experience them fully to earn unique rewards.
This could work similarly to Timewalking, but instead of scaling players down, you’d actually have to be within the correct level range to earn certain achievement rewards. Things like mounts, transmog, and other cosmetics could make this a fun and rewarding system.