DNS only packages would be great for WHMCS. We resell domains through namesilo integrated with WHMCS. However, there is no way to give the customer access to edit DNS when using namesilo's Nameservers. With enhance we could allow them to login to their WHMCS billing account and bounce over to the enhance CP to edit DNS. We have plenty of clients that don't need a website hosting package.
I would add that it would be great if DNS only packages didn't count as a billable website with enhance. For most domains we only make about 1 dollar month so any added fees for DNS only plans would make it a non starter for us.