RDS doesn't scale at all. The performance of RDS won't exceed that of MySQL running on a "Quadruple Extra Large" instance (because that's what RDS is).
Ok, but how about a service taking whatever scalable SQL systems the financial or pharmaceutical industry use, even Oracle, Postgres, or Microsoft SQL server, and then selling it as a service similar to RDS?
My point is, I think there is an opportunity providing enterprise-level SQL scalability on a per-use basis. It won't replace NoSQL systems, because there are some problems where they're clearly better, but it could be done and provide relatively-affordable, scalable SQL access to startups.
