Hey,
first: I think it’s great what you’re doing and I hope to get involved in a constructive manner.
My topic:
I’m running an owncloud server as a collective venture based on principles of the solidarity economics.
I’d love to see a good implementation of some kind of registration-app that allows the admin to accepct/decline registrations.
With that feature I’d be able to convince my admin to migrate sooner than later. 
Keep up the good work!
Fabian
Have you had the Chance to check whether this works for you
https://apps.owncloud.com/content/show.php/Registration?content=170608
Hah, I was just adding a reply myself in order to add the link.
I found it but it lacks the admin accept/decline option.
Right now, I’m using SlimeSurvey as a registration tool. Kind of works but it’s of course thought for other purposes and I’d rather use an integrated solution.
I use this app, but it wuld be nice to have an implamentation in a NC/core 
What I do is that the default user gets 50MB of storage, I call it the demo account, and then once people paid, I can increase to a reasonable data amount.
That’s a nice workaround. I’ll consider using it until a “real” solution is provided.
Hi, I’m the developer of Registration, I’m looking into porting it to nextCloud, stay tuned!
Great!
Do you need financial support in order to take care of the port and to extend the funcionality?
This would be a great addition. I also find that when I select to add a new user to a group in the admin panel, it does not save.
Donations are always welcome, more donations will push me to put more time on this project. If you would like to donate, I can add donation information to the readme.
Hey,
are you referring to the app or a potential bug in the main own-/nextcloud admin panel? in the later case you should head over to the bug section. 
Cheers!
Please report the bug on github and provide browser console logs there.
Since 0.2.0 the app is compatible with Nextcloud!
I have resolved this issue based on comments from another GitHub user about
a week ago. Thanks.
Joshua J. Meunier 「ジョシュア●ミュ二ェ」, A.A.S. Computer Support and Networking
Specialist
meunierjj@gmail.com | jmeunier@joshuameunier.com