This could help a team of developers working on a project to collaborate on a design (real-time multiuser table editing maybe?) or keep track of revisions/branches to the data model. Think Writeboard for databases. Make a premium version that generates change scripts and sell it for $10/user/month. I wish I had done it first! Great job, Mr. Žára!
I keep the DB schema of my current project open at all times. When I change something in the database, I immediately make the change in SQLEditor (and vice versa). This is a recent change in my workflow, but so far it has reduced errors when moving from our development to live environments and reduced the time needed to look up obscure fields or relationships.
Why don't you make it a business, Ondřej?
Btw. you also did some pretty amazing other stuff