You just can't build anything new based on CockroachDB now, because the pricing for self-hosted is "Contact us". So if you build a product you'd need to contact them first and kinda guess how successful you'll be. Maybe it's fine and the license cost isn't a big deal, or it will completely ruin your business case.

Plenty of us have had to deal with this scenarios before with Oracle. Cheap or free to get started, then your product takes off and Oracle shows up and starts to demand their cut. I'm not suggesting that Cockroach is the new Oracle, but this type of licensing introduces a significant uncertainty into your future plans.