I don't really see the point of starting with NoSQL and then going for Oracle. NoSQL DBs are real tools you know, not toys you through after your app gets traction. It's actually the contrary that has happened so far.
Maybe I should have been clear. You only go to SQL RDBMS if you need it. Which, in the vast majority of cases you will not. Further, you only go to SQL where you need it.
For instance, right now someone is developing a street car racing game for Facebook. The XBox kind, not the FarmVille kind. At any rate, one of the features is obviously, playback. Now keeping all of those physics updates in an SQL is pointless. And figuring out a schema for that data would have only gotten in the way of them getting that out the door. Throw the physics messages in a queue and write them to Cassandra. If you have even 10000 MAUs, you will easily generate billions of rows. It's just not data that really needs to go into mysql.
I don't think Cassandra is a toy. I think you should 'get it out the door' with everything in Cassandra, and then slowly, move the business stuff off. User names, what cars they bought for instance. Stuff that is not read often. But at first, get it out the door. Don't stop to figure out a perfectly normalized schema with balanced indexes.
Isn't Cassandra slightly more complicated than MySQL? Sure adding another column is trivial, but the access patterns & indexing need to be determined first.
