Speaking as someone with good insight in enterprise NoSQL sales - vast majority of revenue is coming from Fortune 500s shifting off oracle systems.

Oracle customers have been very easy targets - solve the technical problem, and then give them sales people that care about their success and support people driven to solve any hurdles. I've been on the phone with ex-oracle DBAs crying from happiness, trying to explain how working with a support team that's genuinely there to help them get their job done has changed their professional lives. Those people become lifetime advocates and friends, making up a foundation that will keep the current NoSQL winners healthy businesses for a generation.