That's exactly what we used in on usenet (except,without rendering unless you were using a nice GUI reader, not just tin/rtin)

The problem is that that's too many characters to reserve (they all have to be escaped when you want the actual character) making the resulting text look awful in plain text mode.

  +strikeout+

  ~code/monospace~

  _subscript

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I see you, mlok, you fellow person of culture :)