What if relays add support for ads only for the users that are not paying? It can also be incorporated at a protocol level, so that clients are also aware of each relay's ads (for better feed ordering) and maybe also report back to the relay impressions and clicks per each ad.

That way, relays could monetize ads from publishers only for people that are not subscribing. And the ads won't be targeted as they currently are on social media these days, because the relay doesn't know anything about each user's identity.