Just another plugin idea....

Well, I am a noob...sad to say...However, it needs to be stated. Because, I am not sure if this is a new wonderful plugin idea or just an old outdated idea that I just thought of...get it? Anyway, when I saw that you guys took suggestions from your users and actually used the good ones, I thought...

Well, they already have all the good ideas taken up...so, no, I don't have any ideas.

But that is because I was unfamiliar and to newish (is that a word) enough not to know that a multisite network doesn't allow for private registrations on subsites.
This is a problem.
I have a plan that needs to have subsite registrations that do not in turn register the new user on my main site nor on the 'network' sites.

So here is the question/problem...Basically, how do I allow my subsite admins to accept registrations to their own site without being connected to any other subsite?

Ok, fill in the plugin name here: multisite subsite private registrations plugin by wpmudev

Get it?

I have to imagine that this would be a wonderfully accepted plugin for the masses. With that stated, I worry that I am not the first to suggest it...and if that is the case then why don't I see a plugin for it...right??