Cool idea, but a lot of people would probably wind up hating it if they decided to do this. Not only would it take a lot of dev time to do this, disabling aetheryte access will definitely cause an uproar among the playerbase due to newer players needing to go through the MSQ to access quests and other duties. Not everyone would want to opt into an event like this, and forcing players to participate will just do more harm than it's worth. Plus, with more casual players who don't want their experience to be interrupted will be forced for their progress to be halted. It's just way too much hassle for a lot of unhappy players that the dev team wouldn't want to go for.

Would be fun though, but only if aetheryte access and MSQ progression/crafting aren't able to be interrupted as well as keeping it outside of the city states so they could be designated "safe areas". Perfectly fine if it's restricted to only areas outside of the city states. It would get people out in the open world again doing something aside from the occasional old relic weapon grind.