A domain owner user can create subservers, as many as you allow them to, and those sub-servers can have any name (it is not a “subdomain”), and can have any feature (again, it is not a subdomain) that a top-level domain can have, including mail, web applications, databases, etc… The only difference is ownership and where the files go. A sub-server is owned by an existing domain owner user and the files go into /home/domain/domains.
I don’t know how else to say it. It sounds like you’re still thinking Virtualmin is like cPanel. It is not. If you want cPanel, buy cPanel. But, if you want a domain owner user to create other domains, they can create as many sub-servers as you allow them to create with any features you want to allow them to use.
And, I’ll add the reseller accounts in Virtualmin Pro do allow creation of top-level domains by the reseller user, again limited in whatever way you as administrator choose. If that’s the user/domain model you must have to be happy, then Virtualmin Pro starts at $7.50/month or $75/year. It is intended for people who make money with Virtualmin…if you sell hosting and make money with Virtualmin, we’d like a small piece of the pie.
Virtualmin GPL does have the ability for users to create domains, though, so even if you don’t want to pay for Pro, you already have what you’re asking for…it just looks different than what you’re used to.