Thanks for the responses. I wasn't really asking for how to do it, I was just asking if there is interest in such a service that would work entirely online..
you ARE asking how to do it, if you don't want people answering that question then change your title to a better one.
Imagine something like a coinbase without a KYC, just anonymous.
there currently are known services such as the one you have in mind but they all suffer from the same flaw and that is
lack of trust. and there is also a certain level of shadiness to all these online services that makes them undesirable.
its ok to post about it on this forum by the way, you can either post it here or in
Service Discussion board.