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
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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.