Hot take: I don't think that donations are a sustainable model for many use cases, especially like Mastodon being Twitter replacement. But I also think that M does not have to be T replacement. Neither do I think that Lemmy or Kbin should be replacements for Reddit.

If a sufficient number of specialized population currently platformed at Twitter or (especially) Reddit could switch, it wouldn't reach the size where platforms need to earn enormous ad revenue to keep themselves afloat and it also could keep the cat posters and alike out of this place, deep down in the Facebook wasteland or Twitter toxic pool. That would solve the revenue problem and prevent internal degradation as well.