The most important feature is the decentralization here to protect against a data breach, isn't it? I think as for the payment functionality it is very likely that messengers like WhatsApp will soon have such an option, too.
Yes I agree decentralization is our main target and with our architecture in place for the next version (v4 - please check our whitepaper), we will be able to offer a social/im app 100% blockchain based which is from what I am aware of THE ONLY ONE
And will it be fully scalable if you assume mass adoptions in the tens of millions of users? WhatsApp has an incredible amount of data being sent every single day.