What's to stop this from falling into the same trap as always? They grow, user donations aren't enough to sustain them anymore so they have to look into alternative ways of getting money, users hate it, they start a spinoff that promises to be better, rinse and repeat.
Tildes is a non-profit with no advertising or investors, so none of that pressure is there. There's no danger of donations not being enough to sustain it. The expenses are already far more than covered and it could easily stay running in its current state forever.