Work is in progress to support more than four active people in video calls. We will keep you posted.Jay Yoo commented
Zoom, GotoMeeting, Lifesize, Vidyo, Workplace, Highfive, LiveStorm, ClickMeeting, RingCentral, Sampage, etc.
Most O365 users with All these web conferencing services are waiting for this feature to be added.
I'm certain that MS has done their market researching but we are all willing to pay little extra more to have this features added.
Keep up with this update!
Thanks to everyone who volunteered for testing the Office 365 group calendar. The TAP team will be reaching out as we are closer to being ready.