Hello, I think your extension looks useful, but it seems to be lacking the feature I really need for my site:

I am currently setting up a new site for an appartement building where I want only those living there to be allowed to register.
I know the appartement number (4 digits) and the owners membership number for each appartement, and I would like to include two form fields in the registration form where the user should enter these two values.
Then the script would validate against the internal list of allowed combinations and proceed with registering if the combination was found.

Is this currently possible with this extension, or will it be available in a later release?

This is not something that Registration Validator is designed to do, or will be in future. Registration Validator doesn't change the registration process at all in the sense of adding forms fields or similar. If you need this facility, you'd be better using Community Builder or CBE. However, neither of these offers the validation you are looking for (as far as I am aware).

Registration Validator is purely concerned with checking username/email/IP details against spam databases or internal lists.

To be honest, your requirement sounds rather specialised and you may need to look into a custom component to handle it.