I actually hope that some dev work goes into providing “premium features” for paying subscribers. Things like profile cosmetics, awards, “superlikes”, gif embeds, maybe sub only communities/threads. I view all of these as perfectly acceptable premium features that folks pay for on platforms like Discord that don’t deter free users. If it helps make instances sustainable and keeps high quality admin & moderation in place, I would argue it would be a big community benefit.

Another possibility is instance - as - affiliate where the admin sets up affiliate accounts with services like VPN, Amazon, a web host, etc. To enable users to buy things they would already and give a kickback to the instance.