Thank you for your answer.
It's more a production feature (multi-tenancy) to keep customer databases physically separated while simply accessible, more than just a development issue. Having one server and/or one instance per customer on many ports may lead us to a really expensive solution not suitable for our business model.
If we would use some software tricks (labels, index) to separate data, we wouldn't be able to grab some customer/enterprise database to move it, duplicate or simply move it on their own appliances.
Hope we will see multi-tenancy one day in the so great neo4j !
Best regards.