360 Friends On Xbox One List, But Cross-Platform Chat Limited
The universalization of Xbox Live accounts across Xbox 360 and Xbox One was a good idea. It simplifies things a bit for people looking to get Xbox One and has a lot of potential for carrying over friend lists and the like to make the experience social from the start, rather than forcing people to start all over. No one will have to be friendly, since they will have all the friends they made before.
Now Xbox One users will actually be able to send instant messages back and forth with those 360 friends. Unfortunately, despite the messages being sent through Skype on at least the Xbox One side, One users will not be able to engage in video or voice chat with their 360 friends.
Xbox One architect Marc Whitten cited sound quality issues, but it still seems like a fairly arbitrary issue, and one I would expect to be dealt with as soon as Microsoft brings Skype officially to Xbox 360.
Also of note...
As an added clarification, since Xbox 360 only has room for 100 friends at a time, if an Xbox One user has more than 100 friends and gets on 360, it will only show the friends they are friends with through 360 itself.
All of which means...
Microsoft's talking points regarding the friend list functions seem to be focused on the social 'feel' of the Xbox One. Whitten talks about seeing your friends online and feeling their presence. You can see them, they can see you, you can both tell what the other is doing...
...but that's about it. A total lack of cross-platform play is a bit frustrating, but only expected on a console that is not backwards-compatible. Not being able to engage in voice chat with a console that has provided its own voice-chat services in-game for years seems to stretch the plausibility of Microsoft's explanation of technical problems.
As with so much else in the coming console generation, this looks like a decent idea that just isn't quite carrying itself as far as it probably could, but Microsoft consoles do tend to update frequently. Perhaps the full potential will be realized sooner rather than later.