Launched these guys and many other OSS cos and I never thought of them as a true DB. Rethink was evangelizing an approach and how DBs of the future should operate. Ultimately no one knew if they were an DB or a load balancing engine of some kind that sped up DB transactions for say mobile apps that would only send DB changes to the client vs entire DB data. They got stuck in this no-mans land of no one knew what they were - let alone they had no way to sell it.
Open source or not didn't even come into play, They had great interest, devs liked them and they figured out how to do meetups without much budget. Devs I knew said they liked them team but shortly into it it was clear they were hoping a revenue stream would stick and went forward on that would just happen. Strange one really.