Google talk/hangouts chat still works and does this. Although you are also correct in that case as Google is distracted and doesn't care about Google talk. An

Google talk/hangouts chat still works and does this. Although you are also correct in that case as Google is distracted and doesn't care about Google talk. And of course fragmentation-- Even if Talk, Signal, Whatsapp and Telegram all support discovery and upgrade, the network effects (or lack of them) kills it in practice.