Quote from papa_funk »
The truly eagle-eyed among you may have noticed that 903.10 was removed from the Comprehensive Rules (and 903.11 bumped up to fill the hole).
It's such a small change we were just going to let the Comprehensive Rules Update Bulletin make note of it and move on, but, for whatever reason, the change didn't get reflected in the Update Bulletin, so we're mentioning it here for posterity.
The old rule handled a Commander getting exiled face-down in a situation where a player could look at it. They were obligated to do so and return it to the Command Zone if it was a commander. This was to deal with various corner cases that let you grab a Commander out of a player's library and keep it exiled face-down forever.
With the removal of tuck, this became a corner case of a corner case. I don't think it's possible to make it happen without assistance from the owner of the Commander at this point. That's not a rule that's earning its place in the rulebook, so we've removed it.
In the unlikely situation that you do find yourself with your opponent's commander face-down in exile under your control, the removal of the old mana production rule makes it clearly correct to play it and beat them down with it anyway.
Quote from Sheldon »You're the reason we can't have nice things.