I think that's a great idea. Definitely a great reason to pick this game up again.
Although, we must consider AiGrind, and the fact that this would make them lose money.
Here are things I'd try (one, or two at most, not all of them at once):
- one season lasts only 1-4 weeks, and new one launches every 1-3 months, so we have to go back to regular servers (I personally remember that I kept playing for a month or two longer after the "fun" period ended, so there's that)
- make it pay2play (like the good old times), could reward best players with free codes for next season
- some sort of transfer system? transfer your characters to regular servers after season ends, or ability to transfer 1-2 items to next season
- reduced prices for MC items to encourage buying cosmetics that'll soon expire
Server itself could use heightened drop and mob respawn rates, maybe doubled arena/dungeon entrance limit, general QoL changes to make gameplay on such server more dynamic and user-friendly.