We are tracking requests and interest in this functionality within this thread on our feedback wall : Multi-database capability in Neo4j 4 on Aura | Feature Requests | Neo4j Aura
The update is that we are still evaluating the right capability within a DBaaS to meet the need you highlight.
While multi-tenant multi-database is the right solution for on-prem where you have outlaid a large cost on hardware and want to maximise value, and already have taken on the overhead of resource management, in the DBaaS that doesn't make as much sense. The need for most customers in the DBaaS context is met by an API for database management (creation, update, delete etc) in Aura and some form of Pausing capability. Whether that is a standalone database, or a database in a database, is an implementation detail of no real relevance.
DBaaS already mitigates the cost concerns (no outlay of capital expenditure on hardware and only paying when you have a database running) and the resource management overhead. Giving folks multi-tenant in a single Aura instance actually transfers back some of that resource and capacity management overhead back to users, going against the value proposition of DBaaS.
Please add any additional comments to the feature request and we can continue to lean on that for input during our decision making.