Yesterday, an employee of Wizards of the Coast published this thread to the Magic: The Gathering forum on reddit.com, concerning a rules update that would go into effect with the release of Eldritch Moon. The proposed update affects the ability of players to view their own sideboard (an additional fifteen cards that players can use to make substitutions with from their main deck) during game play, as well as the sideboard of any players that they control.
The rule presently reads as follows: "During a game, players may look at their own sideboard and the sideboard of any players they currently control. The sideboard must remain clearly distinguishable from other cards." This rule is found in the official Magic: The Gathering Tournament Rules, section 3, subsection .15.
Starting with Eldritch Moon, this will no longer be the case; players will no longer be able to view the sideboard of their opponent, even if they have control over their opponent due to cards like Emrakul, the Promised End, or Mindslaver. The Wizards of the Coast employee, Matt Tabak, specifically says that the rule in its previous form caused issues with informational access to an opponent's cards, strategic player concessions, time-delays due to note-taking, and other gameplay inconveniences.
In addition, if a player tries to force their opponent to cast one of the "Wish" cycle spells, such as Death Wish or Cunning Wish, they will be unable to cast spells from the sideboard of that opponent (the Wish spell will still be exiled though, as failure to find a target still results in the card being exiled).
This rule change will also affect Magic: The Gathering Online once Eldritch Moon has it's delayed digital release.
Interestingly enough, Tabak deleted the reddit thread he posted concerning this rule change. It's possible that an official announcement will be posted on the Wizards of the Coast homepage closer to the Eldritch Moon release.
Stay tuned to TechRaptor for further coverage of Eldritch Moon and all things Magic: The Gathering.
What are your thoughts on this rule change? Do you think it was necessary? Let us know in the comment section below!
[Edited June 27, 2016, to fix errors regarding legal targets for the Wish cycle]