You see it today with drivers having both Uber and Lyft apps open.
By now, most people in Europe also have Messenger, but still mainly use WhatsApp (slightly generalising). I think that primarily comes down to WhatsApp being a much better messenging app. It's quick, reliable, easy to use, power-efficient, small, well-integrated into the OS, secure, and most importantly: media sharing just works.
We also have a low WhatsApp adoption rate. Lately fb-messenger is winning territority (and so is snapchat, but for other reasons), since it offers good group chat on top of a service that already covers north of 80% of the entire population.
In which country? Because I have tons of messengers installed and so do most people I know outside the US.
Sure, I have messenger and hangouts and telegram as well, but WhatsApp is like a primary mode of communication.
WhatsApp on the other hand, is more trusted than Email - When some friend sends me an email, he asks me via WhatsApp if I revived it.
Group Chats, especially with younger folks, are numerous and used for anything, even though the technology is obviously lacking, when compared to other platforms.
But most people either don't care, or perceive these benefits as less important compared to the network effect that WhatsApp has - "I don't want to switch between [random messaging app] and WhatsApp, why don't you just accept what everyone uses".
It's practically the same as with Facebook in the US, and just as bad.
I was in Germany two weeks ago and I tried to get my colleagues on chat...any chat...when I mentioned WhatsApp, they all looked at me like I had a unicorn horn growing out of my forehead. So far I have been unsuccessful in getting any of my team on a chat platform on a regular basis. My company supposedly endorses Lync 2010 (yeah, I know), but probably less than 10% of my coworkers use it and the entire division in Germany doesn't even have it installed on their PC's. Our Lync is also broken by the fact that corporate IT doesn't allow it on mobile platforms.
But this mostly shows that the popularity debate is moot - you tend to know/use what your circle of friends does disregarding of statistics of this article posted.
Google was in a position to capture the chat market by tying it to an email service that everyone was using - GMail. But it had two problems: 1. Email is an open service that doesn't lock users in meaning people using Yahoo Mail can still communicate with people using GMail (unlike Facebook where the only place to interact with FB users in is FB). 2. Google didn't lock its users in with GChat, so users could drift away to other services while still communicating with GChat users if need be.
Due to its very nature, FB was destined to win the messenger wars; if all your friends are already on FB then most people will default to what's easiest--the chat functionality that's already there and all your contacts are connected to. But since FB tends to be your personal circle rather than work circle, this left the work circle open, which Google could have captured if it hadn't screwed up on Hangouts leaving the door open for Slack.