The question is who planned this. It is just plain wrong to have many databases on one server.
The plan is to create many databases on this rac so the question is
I understand that for a dba usually it's easier one instance per machine (and a good way to use resource of the machine),Have you considered VM's?
but this is not our case.
About you idea I can add that on the server there is a big instance that should be the instance reserver for all that small applications
that need only one schema. So in a little way we are starting to consolidate.