You may be interested to know that I have implemented conversations in Edu_RSS. It's not perfect, and so far utterly nobody has noticed (and there are far fewer conversations than you might suspect, which means I need a better way of detecting the good ones). Here's an example. But the main point here is that we are now only months, maybe weeks, from a functional system linking conversation threads between blogs - not a walled garden, but something that we can use, we can control, for ourselves.
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