IMHO you can't fund a service with meagre normal banner advertisement revenue anymore.
Someone wishing to fund a Fediverse service would have to write a deep data-mining system that displays personalized and targeted advertisement to their users and get sufficient investment to survive until they have a large enough user-base and scale for their data-mining to turn a profit.
Not impossible, I guess, but given the invasive nature of said data-mining they would probably be defederated quite quickly (if found out) as in a federated network you can't cleanly separate whom's data gets mined.