As a concept, it could be a valid approach. But you need to put actual numbers to see if things make sense:
- What would be the monthly membership fee?
- What would be a reasonable SLA? If there is an outage on a Friday night, are the members okay if they wait until Monday to get it back someone online?
- What do you think is a good hour rate to pay for an admin?
- What should you pay for someone to stay on call?
- Can I run bots? How many? Does each bot count as a separate account?
I think you'll see that as soon as you start asking people to put money and to feel like they "own" it, the demands will increase and so will the costs.
For reference, the one coop I am somewhat familiar is from Mastodon: cosocial.ca. Each member pays CA$50/year for an account. I think this is particularly too expensive. There are other cheaper "commercial" alternatives that charge less:
Now I am confused, are you able to make changes to the Lemmy codebase? A fork? If you want to find a way to fund development, why not just work with the current team?