In a similar vein to how you have made cockroach multi-tenant, not too long ago I worked on building a multi-tenant sass version of a business intelligence app. The app uses a relational DB, initially we used separate schemas on the same db cluster, but we had problems with noisy neighbors, as well as concerns about it's security.

We later opted to run dedicated database clusters for each tenant, however it greatly increases the marginal cost, and makes it difficult to provide a free tier of service, which is a valuable way to gain new customers.