In short, Middle Earth 4K box set will include; the same 4K release available now, some Blu-Ray coasters, not all previous extras, a new extra, some tat.
The middle earth ultimate box set will have both Lord of the rings and hobbit films with Theatrical and Extended cuts on both 4K UHD and Blu-ray
The hobbit Blu-ray discs will be same as previous so no loss of extras for those films
It's Lord of the rings that is getting new extras and will also be using some of the previous extras
To me the 4K steelbook box sets not having Blu-ray versions of the films and no extras means the 4K Middle Earth Ultimate Box set is a better option and be nicer looking overall
Blu-ray ray discs with films and extras are not coasters and that applies to all Blu-ray releases
There is a LG 65 inch 4K TV in my home and Panasonic Plasma TV and a Sony 1080 Projector
My Panasonic 1080p Plasma 3D TV the picture quality is excellent especially for films
Some homes have multiple TV's so Blu-ray discs included with 4K UHD releases the Blu-ray discs are not coasters but actually used a lot in homes