We don't have the capacity to implement all the features users ask for, at least not without additional contributors or waiting a long time. So it's better to implement it as a bot.
The cleanest solution seems to be the one described in my previous comment, so you get an archived community with all the original content, correct usernames etc. And make a new community for new posts. Or have the bot create new posts and comments with the same content, and credit the author in markdown body. But that seems like a worse solution in many ways.
