Certainly, the idea is an exciting one. However, what would be needed is an quick and convenient way to link articles together that makes it clear from the outset that one is a respone to another.
Currently, I can mention someone's name and put a link to their article in a response, but this does not flag up the reply to anyone else who might wish to follow such a debate/conversation. A way needs to be found to do this on the landing page or daily email. Clearly, the comments section cannot be made too large for a variety of practical reasons.
In the matter of blocking, there are people out there who specialise in the attack ad hominem and there are no depths of vitriol or personal insult to which they will not sink. They will also pursue individual writers for the sole purpose of harassment. Not all of us have the thickness of hide needed to shed this sort of thing, so the block needs to stay..
To me, one of the wonders of Medium is that, amid all the PhDs, professional journalists, lawyers, business people, critics, artists, published authors etc, there is still room for a bloke like me. A Bear of Very Little Brain with nothing but a humble Bachelors' degree, 64 years of life-experience, an intense curiosity, a reading habit which has covered 'many a quaint and curious volume of forgotten lore', and an attitude! I expected to be booted straight off with a curt "You don't make the cut!". Instead I offer my thoughts and some people even read them!
If Medium became what you say it could be, there'd be no room for the likes of me!