How to manage O365 Group membership through AD Security Groups and/or nested O365 Groups?

I have two issues concerning management of membership in Groups:

1. In the Outlook Widget, I see that I can add another O365 Group as a member in an O365 Group. But what does it mean? It seems like I am then adding the individual members from the other groups as members, not the Group as such? Or is the meaning of this that I should be able to manage individuals for instance in a "mother" group, and then add the group itself to another group as a nested group? Why don´t I then see the group in the membership list?

2. Security Groups and mail-enabled security groups seems to be a better way to manage a company or department team on a regular basis. But it does not seem that I am able to add an AD Security Group as a member in an Office 365 Group. Am I missing something, and/or is this on the roadmap?