Ok...
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Are you suggesting that a Facebook group could handle that?
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Web forums exist (the kind that were completely ubiquitous 25 years ago). They're a great way to handle a large number of concurrent conversations.
You can still use robust hosting solutions that can handle a lot of traffic, but the advantage of controlling the site yourself is that if wordpress decides to take it down, you can just host it somewhere else and have it back up the same day.