It sounds like Kaizala does exactly what teams does, just with the ability to do it in groups of up to one million.
I doubt anyone will need to communicate with one million people.
I work for a company where we are required to use Skype and Yammer. Skype is handy for video conferencing, but beyond that, I don't have any company owned portable devices, so only have it on my company owned desktop. As such, for day to day use, it doesn't do anything that my desk phone can't do. We even switched to IP based switchboard a few years ago, so I doubt Skype would even save them money. If my company want me to use Skype on portable devices, they can buy those portable devices for me.
I think this system is going to be loved by Management and employees will be forced to use it, but I think for employees, it's going to go the same way that Yammer and Teams seem to have in most companies, and become yet *another* system they have to remember to check for messages on.