As long as capitalism rules the world it's inevitable that free or mostly alturistic projects will fail. Unless you have a wealthy benefactor or find other sources of income.
The original Flattr was a good idea, but the non-success and shutdown shows that people are absolutely not interested in donating without getting something in return.
The original Reddit gold, although flawed, was a good way to support a platform and show appreciation to a certain contributor.
Maybe a similar system can be implemented where the owners and maintainers get a small cut each time a "gold" is bought and given? But then the question becomes, who will administer that...
Crypto/token-based incentives in any form will likely fail because of value speculation.
Perhaps voluntary paid subscription is the right way to go? Get a nice acknowlegement on your profile, and the ability to double upvote a limited number of posts and users? Perhaps access to advanced (own)user statistics? Customizable interface? Templates? Basically cosmetic DLC with a couple of perks.