Considering both that spam needs to be blocked and that relays need revenue to keep operating sustainably, charging a small fee (around 1 satoshi) when publishing a note to a relay seems like it would satisfy both perfectly. But precisely because it satisfies both so perfectly, isn't there a really high chance it becomes a relay where nobody can post anything at all?

Should the relay operate a mint, with notes attaching ecash when they're published? Since there will be cases where people specify too many inbox relays, maybe only include it in a couple of the inbox relays?

Would there be absolutely no one willing to pay to post a shitpost? Would client complexity go up too much?