We tend to gloss over the fact that when dealing with OSS:
- Project maintainers can leave/change/stop supporting the software and the idea that "since it's OSS, I can just pick up the slack" sounds better in ones head, then it does in practice.
- Even large projects (think Angular) can move in odd and unexpected directions, which in reality simulate a company "going out of business" for all intents and purposes.
- OSS 'support' is great, until it's not. Meaning, if there are plenty of SO questions and answers, it's great, until your specific issue isn't addressed, at which point you're either looking to a third party to pay for support, or you're rolling your sleeves up and digging into a codebase you have no experience with outside of an external API level understanding.
The dirty secret of large successful companies is that they actually pay for software, and the support of that software because they understand that time = money and vice versa.
After using datomic in production, I'd welcome my competitor to use Postgres. I'd even push them to. It's a monstrous competitive advantage for me.
There is an "open" strategy, when you offer the core part of your cool thing widely (cheaply / freemium model / for free), and profit from only e.g. 10% of the users that buy premium plans. You also have a fair chance to make your better way of doing things predominant, and put in the hands of a lot of people that won't pay you either way.
The point is that when your cool thing may have a really wide adoption, with the "open" model you may have e.g. 50x the market share of the "narrow niche" model, and thus 5x the profit. Increased mindshare also helps further adoption. This, of course, depends on the adoption rate and paying customer rate.
Haven't you noticed the popularity contest going on with computing?
If datomic isn't popular it will disappear.