This is a pretty interesting situation to me. I may not have everything completely right with all the new PS rules this year, but it looks like an absolute steal for Cowboys if it works out the way it's looking.
This situation breaks out into two parts and is also full of speculation on my part, but we'll see.
Part One: Carr as a Player
Carr seems to have played pretty well as a safety last year, but I think we know he won't necessarily be a game changer, but if what Fish is saying holds true, then the risk is so low that it doesn't matter. If Carr is agreeing to be a PS player, then he doesn't even take up a roster spot. This year there are allowances for 2 players to be brought up from the PS to the team to play each week, then moved back down. This essentially gives us another viable option to put out there without it even costing us a roster spot. I do find it shocking the Carr would agree to this, but it gives us the option on game day to put him in. Another bonus is his locker room presence and his mentoring ability without a roster spot being used or any significant money. If this comes to pass, it's a big win.
Part Two: How it relates to Earl Thomas
If the agreement is in place where Carr somehow agrees to be a PS player for Dallas, then it is also obvious that the staff would pick Carr's brain for a genuine view of the Earl Thomas situation. Carr is well regarded as an honest and stand up guy and would give his true opinion of the events. To a point that if Carr gives the ok, then I think Dallas would also make that move. We have heard enough stories that the "team" wanted Earl gone, but we also know that the team is made up of individuals. Regardless of what the overall vote was, I'd like the FO to hear Carr's take on the situation. If Earl is a bad as has been reported, then I'm sure Carr would back that up and we'd say no to Earl. On the other hand, if Carr provides enough context and details to make Dallas ok with it, then I'd trust Carr's opinion as he was close to the situation.
TL;DR version. We may end up with both of them, and that would be great!