There is a progress. Original answer from Guillaume has implemented and announced in here(avilable since Quarkus 1.8.0): https://quarkus.io/blog/quarkus-1-8-0-final-released/
Here is portion of my java codes.
@Inject
@PersistenceUnit("dummy1")
EntityManager em;
and here is sample application.properties.
# dummy1
quarkus.datasource."dummy1".db-kind=postgresql
quarkus.datasource."dummy1".username=postgres
quarkus.datasource."dummy1".password=postgres
quarkus.datasource."dummy1".jdbc.url=jdbc:postgresql://localhost:15432/postgres
quarkus.hibernate-orm."dummy1".database.generation=drop-and-create
quarkus.hibernate-orm."dummy1".datasource=dummy1
quarkus.hibernate-orm."dummy1".packages=dev.tkhm.graphbff.infrastructure.dummy1
Also you can check the detail here. https://quarkus.io/guides/hibernate-orm#multiple-persistence-units