I will skip the whole sharing thing since we don't know exactly how taht was going to work, but it most likely would have been awesome. Here are some of the things I can think of.
1. Disc based games do not sync with the cloud or show up in your library profile
http://www.engadget.com/2013/06/19/xbox-one-drm-marc-whitten/
Going to a friends place to play Halo 5 which you bought on disc? You will have to have your profile on a USB if you want the controller profile or game save to be there. Your digital profile will not have your settings for this game available.
2. Fragmenting of a gaming library
Only digital purchases show up in your profile. If next gen consoles are backwards compatible or there is no next gen much like there is no "next gen" for PCs, your gaming library will be partly digital partly disk based. If disk drives go away, so does your gaming library
3. Digital purchases can only be made on xbox Live.
For those that want to avoid disks like the plauge (like me), they can not take advantage of Best buy and Walmart clearances of games to buy digital games. Retail bought games are locked to the disk and not my Xbox Live ID. Intead the only place we can hope to get deals from is Xbox Live marketplace.
4. Disk swaps and verification checks for no functional reason other than to enforce DRM
Self explanitory. I'd rather have internet do something so I don't have to.
5. Gamestop and Publishers can keep screwing users with used games and passes
Gamestop loves the new direction Xbox One is taking. Wonder why...
http://gamrconnect.vgchartz.com/thread.php?id=163044
