While this may work, and would work on me if I really did love the project enough, I think the fact that a lot of companies use big, scary language like this (the most notable example is Wikipedia) means that this isn't a well-received option anymore.
"This app requires community sponsorship and we're trying to raise $20k in April 2019 or there will be no new releases and we will close the project."
One way to look at it is that if people can't pay or won't pay then they don't deserve it or they don't care.