Add Unity client to Teams conversation

I read about the Graph API which seems to be the only API available to create apps for Teams with. Unless I didn't get it right, it looked to me, that you could only write apps the are getting installed into teams.
I was wondering if it would be possible to integrate clients using the Unity Game Engine to participate in Teams meetings.

My guess is you'd need to write an app for teams that handles the interop with the Unity client.
Is that somewhat correct?
Do plans exist to provide an integration API for Unity, now that HL2 is rolling out, so you can do this?