You had the ability in EE3 (in a pre-release) to import registrations using a csv file.
This would still be a really really useful tool. In my case, we have an application process, and then jury the results before we allow folks to actually register. It would be so much easier if we could import that data, rather than having to enter it all again, and then send actual invoices.
It seems in reviewing the forums that others have interest in this as well.