There are a few ways to monetise the Fediverse.
- Donations - to devs and those running the instances. Lemmy gets enough from donations and grants to have a couple of full-time devs but it still doesn't pay a lot. dansup using Kickstarter is proving interesting. Donations to your instance works well and a lot of places that offer this bring in enough to cover hosting costs but not much more. Open Collective has proved very good in this regard.
- Classified ads - [email protected] does a decent job of bringing buyers and sellers together.
- Subscription newsletters/blogs - Ghost is moving into the same space as Substack but with federation, so should do well.
So you wouldn't be able to give up the day job by running an instance but you might if you were the lead devs of a popular service or if you had a thriving following on Ghost.