I'm contemplating a multi-tenant SaaS application wherein each client would have its own allocated database with its own client-defined schema. None of the underlying clients would have a large scale of data by themselves (likely in range of 1M rows on avg across tables). Some latency in processing would be fine -- this does not need to be real time / is not serving e.g. live web apps. And from the client's perspective, this would be serverless / manageable by non-technical users.
All the commentary / technical blogs I read online (understandably) discuss scaling databases into a large number of rows (with e.g. horizontal sharding on primary key, vertical scaling into high-powered servers, etc.). While scaling into more DBs is not discussed, it feels like an easier thing to tackle because the data within a single DB doesn't need to be split... Each DB can live on its own next to other DBs on a single server. Just a matter of routing queries.
Are there any databases that you think would well-support what I'm talking about? Or any combination of things like Vitess/k8s that might be able to do this database / query routing, maintain each of the underlying DBs, etc.? You can see PlanetScale.com has built something like this, but they're a bit more knowledgeable having literally written Vitess... Same comment on MongoDB Atlas, but Mongo's product does not obfuscate the underlying servers.