I've done this in the past and always felt that it was not an intended use of the dining plan whether Disney took out the old language or not - I definitely see an application of the basic, perennial "non-transferable" language meaning you can't use your credits for other guests, so despite the lack of enforcement and the removal of the more clear cut language several years ago, I think it's totally in their prerogative to not have to announce the end of something that was never an official policy. More or less, I have always assumed we could run into someone not allowing us to share every time, and although I'd be disappointed I wouldn't have been surprised if I had encountered this on a trip. (Not that that doesn't make it financially frustrating having spent the money with the intention to share)
Sure, there are people on the Disney parks mom blog who have said you can share, there are plenty of Cast Members who have said sharing is allowed, etc - but even now Cast Members are continuing to say that you CAN do this in writing to guests planning their trips and then the actual restaurants are saying it's not allowed. That, for sure, is a very regrettable guest services problem and I would hope anyone who has it in writing from a CM who told them that in error would experience an understanding staff at the restaurant and that they would allow it given the circumstances.
I wouldn't be surprised if enough people have learned of the mathematical benefits of sharing a DxDP across two rooms and Disney finally felt like things have gone too far. For my family, if we get a dining plan we will only get the DxDP, and only if we can share it with more people than are staying in our room. Otherwise, it's just cheaper to pay out of pocket and not order as many appetizers and desserts. This will definitely change the way we eat and order at Disney - I feel bad for the waitstaff because this will surely yield smaller checks, and we will probably choose to eat off property / get groceries to help soften the blow of $45+ entrees. In short, our party of 6 will spend LESS money on Disney food because we will choose to find better value elsewhere during our trips. Maybe that's what prompted them to ease up a few years back, and maybe that's what will cause them to soften this policy a few years down the line - only time will tell!