The APIs are all public. The company can build whatever integrations they want to offer. For example, many already use EC2, VPCs, S3, Lambda, Kinesis, etc. to extend their databases into a client's architecture, and it's no different than what AWS provides.
Disclosure: I build EC2.
If this is a million dollar idea, I'm just going to give it away I guess, so here goes nothing in explaining it!
Imagine an AWS/Google Cloud like company that only sells B2B, so Cockroach for instance, could pay this company to host their own cloud offerings, plus sell through other cloud offerings of the said B2B service but under their marketing umbrella. The B2B service gets a nice chunk for administration et. el plus some fixed percentage of gross (maybe? i dunno what it'd look like).
I think if you contractually obligate yourself as a business to never sell cloud services directly (only via partners like, in this instance of theory, cockroachDB, but it could redis, mongo, whatever), it'd be a fairly stable and comfortable arrangement.
Could also be a way for other SAAS companies to buy into infrastructure without indirectly funding a potential competitor too.
Maybe its too complicated to achieve, though.
There are several companies that do managed services like Aiven, IBM's Compose, ObjectRocket, etc so it's possible for them to get involved like this... and it looks like ObjectRocket just did that for CockroachDB: https://www.objectrocket.com/managed-cockroachdb/
I don't see why a startup would have such a problem with it, especially when they control the software as well.