I think they're talking about one-schema-per-tenant, not one-database-per-tenant like e1g.

Still, we'll never hit anything close to 1000 customers per server, we distribute them over more servers instead. In fact, that's an advantage of this model over the single-database one: since every tenant is isolated, the model is perfectly horizontally scalable. You can simply fill up servers without worrying about massively distributed databases or datacenter-wide load balancing. Hell, we just migrated across hosting providers with barely breaking a sweat: we simply moved machine by machine without ever worrying about latency between DCs and all that.

But if your schema changes, it means you have to do a migration to N databases (N being the number of customers you have). If you have to update your database from PG 9.0 to PG 10.0, you have to do N times. And so on. You'll have N number of backups that all have to be stored individually. Etc etc.