itsonlymuni,
You are correct with your question "Which begs the question, why would he convert his preferred to common and then dilute his own holdings?"
IMO, Mark already has the necessary votes to put this RS through, from his financier friends, borrowed shares, etc. Why else would he NOT publish the company's intent to do an RS, and, hold the meeting 4 days before Christmas, if it were not a blatent attempt to make sure dissenting shareholders were at a minimum.
And you are right again with your supposition "He won't convert until he has cleaned up the debt at the expense of shareholders."
The RS that will be critical for everyone will be the one after this one. By then the books should be cleared of debt and after that RS Mark can take Preferred shares for salary owed, then convert and take total control.