I like the idea in theory but in reality the number of people who can get a somewhat complex backend running on their own is small and the reward (syncing notes) isn't really that compelling so I think it isn't a great idea...

Instead of sun setting the app I'd switch it over to use iCloud (free backend), make it free, and set up a public support forum. This way it'd work and there would not need to be any ongoing investment of time or money.