Everyone? At once and next week? It would just die.
Kbin.social had a nice post (check their meta community for it; it’s technically a different software, but still), how the instance went from costing $2-3 a month to 1000. And that’s a tiny fraction of reddit.
Development needs to advance just to better handle current user counts, there’s a lot of things that simply never were an issue when only a few hundred users were active.
The way it will work, is probably donations, maybe some very few paid instances.