4
A reminder in the age of the Fediverse: if you're not the customer, you're still the product.
(slrpnk.net)
OP was taking about Tumblr, but I think it applies even more to the Fediverse: users need to develop an ethos of paying to support the sites they use. Otherwise advertisers pay the bills and call the shots.
Devil's advocate here - as soon as you introduce monetization to the use of a service you have locked in it's potential as an income stream which will inevitably lead to the downside you are afraid of.
Fediverse services being distributed means no central host has to bear the entire weight. I could probably take on all of the server load that I use if I repurposed my PleX server:
https://twitter.com/sandofsky/status/1592223884107218944
This is not about money, it is about control.