As studios begin to push the new format, SteelBooks are beginning to emerge. The early releases include both the 4K and standard Blu-ray discs. Sony are also including a 3D disc in some of their 4k releases. This may change at a later date when 4K gets a stronger foothold, but in the meantime, for any SteelBook collector who is planning to upgrade their gear in the future, it may be a good time to add to your SteelBook collection, and future proof your movie collection at the same time.
For many of you Blu-ray will be "good enough" and I get that. 4k will probably be, at best, a niche market, and also likely to be the last disc based media, as more and more people switch to streaming services, iTunes etc. Call me old school, but I still like to own my movies on disc.
Most (but not all) discs will include immersive audio (Dolby ATMOS/DTS:X)
Dolby Vision will soon be encoded to some new releases, and will probably be included in the UHD spec. at a later date.
All 4K Blu-ray UHD discs are Region Free.
N.B. Some of the standard Blu-ray discs included, may be Region Locked.