Comment by SoftTalker

I'd like to see

  *this is bold*
  /this is italics/
  _this is underlined_

Beyond simple conventions like this, I'd just as soon drop into HTML as deal with some other markup that ends up being just as complex. We don't need to allow permutations and combinations such as bold and italics, double-weight bold, etc. these never occur in normal prose typesetting and if you need it just use HTML for those rare cases.