This could be a (partially satisfying solution), but I can have only one
storage domain for ISOs, right?
AFAIK you can have one ISO domain, one export domain and many data
domains; "engine-iso-uploader list" reports only ISO domain.
You can have only one iso domain attached (and so active) at a time. But you can have many iso domains defined.
And the same domain can be defined across different domains
The same applies to export domains. When you select "Attach Export" button in Computers -> Datacenters -> MyDc you get a list of defined export domain among which to select the one to attach, in case you have more than one defined.
Gianluca