Flexifield and other special field support

Hmm, that is a nice request, but this is not the job of field_group i'm afraid.
Field group only contains fields, it does nothing with fields. I think what you need is a kind of field composition that can be re-used within nodes. Don't think there is something out-of-the-box for this (yet).

As of right now, I've found a way to do this using Flexifield 6.x-1.0-alpha5 (http://drupal.org/project/flexifield).

I created a wiki site... But I'm sure the same over all concept of using CCK to create two content types (one to hold the fields and the other to display them) will work for you. So first thing's first, I created my content type (Wiki Page) in which I wanted to have the final display of my content.

Next, I created another content type (Wiki Sections). I then went in to edit this content type. First, I deleted the Body. Then, I created two fields, one for "Section Title" - a textfield; and the other "Section Content" - a text area. I set the label to hidden for both fields. It really didn't seem to matter whether or not these fields were in a field group, as it worked for me both ways.

Then I went back to my Wiki Page content type to add in my sections. I selected "Flexifield" as the field type, which comes automatically with its "default widget for flexifield", set the number of values to "unlimited" and under "Content types that can be used as field items: " I selected "Wiki Sections".

Now when someone goes to create a new Wiki Page, they select the Page title, and then they can create a new "Section".

We need so see if we need to do something extra in combination with other field modules like relation or references.
Investigation needed to add use cases

References is like node reference and user reference in D6 - relation will do the same. Flexifield does not even exist for D7, so no use keeping this one open.

Well i 've set this to active because i am working right now on a formatter that can take the logic of flexifield.
The way i see it, flexifield will probably never exist in D7 as i see no current work on it or steps taken to have a release for D7. So the least i can do, is estimate the effort to take on this challenge.

There's combo field for D7 which will do this - or in the end field collection. BTW, we're talking about multigroup here, we're not doing that at all.