Storage tiers like google drive. First tier should always be free that takes care of 80% use cases/users. Hopefully revenue brings more relays. BUT not like $9.99/month for Damus purple that is too rich.
Discussion
Also relays should have bandwidth (only new notes) tiers among themselves for gossip so they share revenues.
Twitter grows by 12TB per day (probably much more nowadays). The cannot be a free tier. No relay in the world will have that much data lying around for free.
People are talking about only storing motes for 30 days - but that would still be 30 x 12TB - utterly infeasible for anyone to store that much data.
And hence the payment tier that subsidies the smaller less space using free users.
Even just the data for a free tier, and even if just saved for one single day, will be too much for any individual to be stored.
For paid tiers it can work, but those relays must then be run hyper professionally, constantly adding more storage, guaranteeing zero downtime and zero loss of data. Only very few relays will have the expertise to pull this off - and that means, a handful of relays will store everything, and those relays can be censored by the state.