Like a train wreck I must watch 
I seem to recall the Diamond POV being in play a long time ago...and I've got three possible scenarios I was wondering about..Hypothetically:
1) Rachel wins POV, and saves herself. Kathy is put up as the replacement.
Can Matt use the Diamond POV to save Kathy, and put Rachel back up?
2) Rachel wins POV, and saves Brendan. Kathy is put up as the replacement.
Can Matt use the Diamond POV to save Kathy and put Brendan back up?
3) Ragan wins POV, and saves Rachel. Kathy is put up as the replacement.
Can Matt use the Diamond POV to save Kathy and put Rachel back up? Can Matt use the Diamond POV to save Kathy and put Ragan up?
don't have a clue if he could or not,
but why would he want to?
It would be a waste.
One of the showmace is on the block.
Would the brigade vote anyone else off when they have a chance to get either Rachel or Brenden out?
That's what I was thinking JB, although Matt is a little unpredictable and I don't know the use rules of the D-POV. Like is it only good for this week or is isn't it. If he does use it though he's putting a huge target on himself because they'll all think he's the saboteur.
Like a train wreck I must watch
It's good for 2 weeks.
To me it makes more sense to save it for next week when he might really need it to save himself.
Because all the questions stem from just one: how do the Golden and Diamond Vetoes interact? And it's a valid question because this plastic sparkle-glued nightmare is hanging around for another week -- and as per Julie, the two models currently coexist.A nominee saves hirself with the Golden. Can the Diamond be used to put that person back on the block by saving the HoH-designated replacement and U-turning the original nominee back to their seat?
A nominee uses the Golden to send the other nominee to safety. Same issue, except that the Golden holder stayed on the block all along. Can the saved person be returned to the block?
Someone who isn't on the block saves the nominee with the Golden. The user of the Golden is supposed to be immune to instant reprisal at the meeting. Will the Diamond allow Matt to send that user up in the nominee's place?
And here's an extra question which I asked in Spoilers. (No reveals, just speculation.) Could Matt save someone with the Diamond next week and name the HoH as replacement?
Not exactly an issue-free power.
If it's anything like the Coup d'Etat, the HoH and PoV winners are safe, and their safety for the week is absolute. No Diamond PoV changes that. I'm sure the Chenbot's programming will be updated by then to clarify this, but that's my most educated guess.