3rd option "users can register themselves freely" DOES include "users can register with an invitation code"

For example when advertised have said put the promotion code xyz so that it will be automatically subscribed to a newsletter. And will it be possible to know if the radio advertising campaign is relevant?

So you want a field to enter an optional invitation code on the registration form?

Or a field upon registration that asks where you heard about a) the site and b) b2evolution

@fplanque wrote earlier:

So you want a field to enter an optional invitation code on the registration form?

Yes

To add subgroups with blogs, trackers, forum…

And when its members can use one more time this feature invitation code joint secret blog,…

So I will summarize this as: optional "invitation codes" that unlock permissions.

It's an interesting feature but due to limited resources we cannot guarantee to have this in the priority todo list.