How's signal different? It's also in the same position as whatsapp was a few years ago. For the time being it may be better, but surely it is not a long-term alternative?
Amongst many, many other factors, it's a nonprofit foundation, not a commercial company.
Long term, it has backing from people (like the original founders of Whatsapp) who want to see an open solution flourish. Plus people can donate.
Also, both the client and server are open source.