I remember listening to a podcast somewhere (maybe the Major Nelson podcast) and one of the Xbox guys (maybe E) was saying that the reason Microsoft can't expand the 360 friends list is because games (and perhaps other apps) might crash if that happened.  The innards of the 360, the way the various systems communicate with each other, just won't allow it.

Shortsighted design (assuming it could have been designed a different way)?  Perhaps, though keep in mind that in 2005 when the 360 launched, major social websites like Facebook and Youtube were just starting up, so Microsoft may not have anticipated that people would want to have hundreds of friends on Xbox Live.  The 1000 friend limit on Xbox One should be more than sufficient for the vast majority of people.  I doubt most people have that many friends on Facebook.  Only the most social of butterflies will hit the limit, and they'll just be adding people for the sake of adding people, they won't actually be in consistent contact with 1000 different people.

That sucks

Well, if Xbox One can't play 360 games--not even digital XBLA titles, there really isn't much for the two groups to talk about. If you have an Xbox 360 friends list, you still have an Xbox 360, right? Not the biggest deal but still kinda disappointing.

This is clearly a misunderstood information, nothing more.

Even if it's not, I suspect that it will be rectified by the time the console launches.

Didn't they already say your friends list would transfer?

Personally I would just want until the console release.  I am sure MS will have a way for you to import friends from one console to another.  You probably will be able to store that info in the cloud and when you login to the X1 those list will populate.  They can still keep both systems separate as they probably do not work on the same system.  X1 probably is designed with a lot of things the 360 does not so its probably why they are separate from each other.  

@CGI QUALITY
I should had stated "In my opinion" in the message but I agree with you, I just can't imagine why ours friends list won't carry over to the new console. It is a thing that shouldn't be a problem.

This could only discourage upgrades.

Yes they did. Even on GAF people are letting everyone know what was said. It goes like this. 

Once you transfer your profile to the XB1 your Xbox 360 is its own thing after that and your Xbox One is its own thing. When you start to add more friends to your XB1 friends list they DO NOT get added to your 360 friends list. If you want to add someone on 360 you have to log in through your 360 to do it.

That is where Xbox Support gets your Xbox 360 friends list will be your Xbox 360 friends list and your Xbox One friends list will be your Xbox One's friend list.