This looks a lot like Simplenote [1] at its core but adding on additional features that make it super instead of simple :) A big difference between the two though is that Simplenote is free whereas Supernotes is $6/month (free for < 40 notes). I think you could upsell Simplenote users if you had an import/export and a plan that was cheaper (perhaps a 50% discount if you pay for a whole year up front).

[1] https://simplenote.com/