Datomic is 8+ years old and by all accounts has a healthy customer base, it's not like they are in the takeoff stage. But of course they have to keep up like everyone else, especially now that there is competition from the OSS side (Crux).
I remember being very excited by RethinkDB, it was a huge shame to see that go down. I feel like they signed their own death warrant by making a product that was super easy to use and was well documented.. so no support contracts, because simply not needed. Such a shame.
The task of making a viable commercial database in 2020 is herculean and I can really empathize with the team's need to both keep cashflow and have a sufficiently sized deployment to debug against.
Can also say that everyone I've met at nubank are really passionate about the ecosystem and seem like they'll be excellent partners