Like many people, I'd definitely prefer having just one messenger, but now I simply use Signal with everyone that's on it and only have to open WhatsApp a few times a week. This entire thing has to be seen as a process IMO.
Pidgin with a shitton of plugins. If the only problem is the migration, that still works as a single client, albeit with drawbacks and hiccups. (I collected them at https://github.com/petermolnar/awesome-pidgin-plugins and yes, it'll need to be compiled, even Pidgin itself for some of the solutions. There's nothing user friendly about it, sadly.)
On the other hand... the only system I never had to migrate off is IRC. The funny bit of IRC is that it's not private in terms of security at all, but because it's anonymus, it still feels like it.
And so I keep thinking about needs when it comes to privacy: what do I really need in the context of internet communication? Anonymity, privacy, or both?
I don't have a definitive answer.
Still waiting for that to be the case. After 6 years of using Signal, I have a whopping... two... people in my contacts who also use it.
The most common response is still "Why don't you just use Whatsapp?"
Pretty much the only way we're going to see critical mass with Signal is if someone like Google were to make it their default platform for messaging.
Because in the end normal users think about the functionality and price first, everything else second. Privacy? Just a neat-sounding bonus you can feel good about if your favorite app includes it and don't care about if it doesn't.
I think the most important factor here is network effects.
I've been thinking about this a bit, and I'm going to stop short of asking people to switch, and just try to get them to install it (and maybe even get them to casually suggest their friends do the same, if the opportunity arises). It's a hopefully small, risk-free step to take, and the more people that have installs, the more likely it is that "no one is there" will start becoming not true, even if not immediately.