Out of my 356 contacts only 46 are on Telegram and among them 11 were seen recently (let's assume they still have the app). In last few weeks only 8 of them replied to my messages or read them so I'd say only 8 are actively using it (I checked with the remaining :P).
On Signal, there are just 13 and only 3 replied to me in last few weeks. All of those 3 were coerced by me into installing it on their phones after I deleted my WhatsApp account recently. So basically none of my contacts was actively using Signal (the remaining 10 didn't even receive the messages).
No one was on Matrix/Riot and no one installed it even after my repeated evangelistic encouragements and promise of full time tech support. Can't blame them as I myself find it difficult to use the service/app for any non-Slack/non-IRC kinda usage i.e person to person messaging.
One day I checked just for testing and more people are on https://hike.in than on Telegram from my contact book. That was surprising. Didn't try any further and uninstalled it.
Almost everyone was on WhatsApp and almost everyone was on Fb Messenger too when I used them.
My contact book is very generic - obviously not the very tech savvy specific circle but a decent mix professions and backgrounds. Also, I have keep my contact book regularly trimmed and limited otherwise it would have been a lot more than 356.
So, if I have to choose WhatsApp's replacement based on this criteria then there's really no other choice sadly :( Though I do have some hopes from Acton's $50 million.
PS. I had checked one day and around 20 are on Apple devices (shows iMessage option for them but a lot of them might be on macOS) and except 3-4 of them none use iMessage at all.
This reminds me of Viber, a local success in the Eastern Europe.
(I work there)
Yeah, maybe if I want my messages to immediately disappear when I click off the app.
(even the new 24hr period isn't good enough to actually have a conversation with people over text)