I find this interesting - source: digging around MicrosoftTeams powershell and Mikael Svenson's blog post on enabling Teams programmatically. 

What's funny, because what I found strange is when Mikael says this:

The creation of the group itself happens against the /edu/groups which I’ve never seen before, but that’s not interesting.

Because that's the bit I found totally interesting.  Why does the PowerShell need the /edu/ endpoint?
Hop over to Graph Explorer we can play with this:

Comparing different endpoint: v1.0

endpoint: beta

endpoint: edu

It becomes clear why we need the /edu/ endpoint.  It has this bit of information:

The hint that a Team is provisioned seems to be the flag "SkypeSpaces"

Interesting.

Naturally, one would ask.  So if I want to enable Yammer, Planner or PowerBI on an existing Unified Group.  Do I POST an update to creationOptions?

Very.  Interesting.