There were many rumors that the Whatsapp conference calling feature will be looking forward to a marvelous upgrade. As of now, the conference calling feature was only set to a maximum of 4 participants.
If you look at the beta updates of the new Whatsapp, that number might be going up to 8. It remains end-to-end encrypted so security is not being compromised at all. There is no official date of when this update will be released but it seems every participant must update their Whatsapp with the new upgrade whenever it comes, if they want to get the 8-to-8 chatting feature.