Recent notes could be freely accessible and older long tail content could be accessible behind a paywall which can be unlocked by users. This is the most natural form of incentives, if users want the long tail content they should be paying for it. 

I imagine simple relays on VPS that freely offer recent content and pull older content from Home Server Relays upon request (start9 / Umbrel). When older content is requested it stays cached on the public Relays.