Feature request: allow original domain as primary

Hi,

After the excellent improvements since version 4.0 following the discussion on https://premium.wpmudev.org/forums/topic/301-redirects-to-primary-domain I would like to propose a small additional improvement:

I'd like to be able to offer site owners to (temporarily) set their original domain as primary domain. In some cases like when waiting for propagation of DNS changes (or new domain registration) for a mapped domain, it can be useful do have all traffic redirected to the mapped domain before all is well and proper.

I currently I have the option of domain verification activated so users cannot add a mapped domain before it is well configured but even then things can happen afterwards. Like a domain going into suspension because of a forgotten payment, a change in registrar or domain ownership (where it might happen that DNS settings are temporarily reset) or even a change in the IP for the entire network.

Also, it'd be great if users could add their freshly registerd new domain even before it is properly configured, while still having the original domain as primary. That way, whenever the registration completes and DNS changes are propagated, requests that use the domain will at least find the right site in the network instead of showing the network signup page.

Hope I explained that clear enough :slight_smile:

Thanks for a great plugin!