Even if you go to airport and "wait", what exactly are you waiting for?
1) for M-class waitlist to clear?
2) for upgrade award to clear?


If you are simply waiting for M-class to clear, I don't think it's a good idea. I don't see how they will accomodate you, when the plane is already showing full. So, You will go to airport with virtually no luck.

With the 2nd approach, I really am not the best person to talk to. I would recommend talk to MPC to see what they can offer. It's only a flight 2 days ahead, so if there's an award availability, it should be there by now. The only problem is, CX tend to NOT give ANY award seats available if a flight is overbooked. This is for obvious reason --> to op-up the overbooked Y pax.