These were primarily k12 teachers in schools in the US. None of them had particular reasons to use flow charts.
It’s likely that people who need flow charts might be willing to learn that cool text-based tool, so a plugin could have an audience, but I daresay that feature won’t be making it into Core any time soon. 
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Not me. My plugin died a couple Discourse upgrades ago.
Best would be if that site would implement embeds. You can see here that it doesn’t. If it did, you could paste in the URL and a pretty picture would appear right here as when you paste in a youtube page (or similar).