A while back I wrote about Microsoft's Astoria REST-based relational data store in the cloud (or in your data center, if you want it there).
With Amazon's SimpleDB, we're a step closer to making this vision a reality. Now we're almost on track for competition (and sooner-than-later commoditization) of the new world where you don't even need MySQL to store your stuff.
Why almost? Because SimpleDB is not a full RDBMS, but is looks more like a flavor of triple store. Now, a typical (i.e., SQL-style) RDBMS can be built on top of a triple-store fairly easily. So we
could will see a SQL processor, JDBC drivers, and the like, from the community pretty soon.
Another way to look at that "top layer" is to take a REST API like those used by Astoria or ActiveResource [PDF link] and simply implement that. Not as expressive as hardcore SQL, but easier, and probably enough for many applications.
What I don't see -- in the long run anyway -- is applications developing against thin wrappers specific to the Amazon triple store service itself. There's nothing fundamentally flawed in doing so ... it's just that, for a variety of reasons, data storage has evolved very slowly. The relational model is going on 40 years old, but still reigns supreme in terms of popularity, even if it has conceptual or technical flaws when put to work in today's applications.
Given the brilliant data storage alternatives that have fallen flat time and again, I doubt Amazon SimpleDB will change the way people talk about storing structured data. So SimpleDB doesn't need to be SQL but it will probably need to at least be RESTful.