As an educator I would've loved to have this last time I was teaching SQL.

1: No install

2: Ephermal (just reload if you've messed up?)

3: Good syntax highlighting

4: Visual UI to navigate the model

Why to pay for it though? That's a harder nut to crack, the UI is quite nice compared to many I've seen so maybe sell as an addon for those that provider hosted databases, collaborative spaces or as a desktop app. No obvious slam dunks though.