I have been holding off on this post until the slipcased edition had been revealed (cover art, description, ISBN).
Some may go 'but wait! aren't most editions of The Hobbit already illustrated by Tolkien??' Indeed, many do feature some of the artwork he created for the book. Some of the artwork he created. This new edition greatly expands on the included imagery, as well printing the text in two colours, as well as a ribbon-marker (likely white for the standard edition, and green for the slipcased edition.)
Following the 'illustrated by the author' series that began with The Lord of the Rings and continued with The Silmarillion, now The Hobbit will be among them, in terms of design and style. You'll see in this post.
As is my usual custom, I'll provide the cover art, ISBN and description below for both the standard edition and the slipcased one.

ISBN: 9780008627782
For the first time ever, a special enhanced edition of the enchanting prelude to The Lord of the Rings,
illustrated throughout with over 50 sketches, drawings, paintings and
maps by J. R. R. Tolkien himself and with the complete text printed in
two colours.
Bilbo Baggins is a hobbit who enjoys a
comfortable, unambitious life, rarely travelling further than the pantry
of his hobbit-hole in Bag End. But his contentment is disturbed when
the wizard, Gandalf, and a company of thirteen dwarves arrive on his
doorstep one day to whisk him away on an unexpected journey ‘there and
back again’. They have a plot to raid the treasure hoard of Smaug the
Magnificent, a large and very dangerous dragon…
Written for J.R.R. Tolkien’s own children, The Hobbit
was published on 21 September 1937. With a beautiful cover design, a
handful of black & white drawings and two maps by the author
himself, the book became an instant success and was reprinted shortly
afterwards with five colour plates.
Tolkien’s own selection of finished paintings and drawings have become inseparable from his text, adorning editions of The Hobbit
for more than 85 years. But the published art has afforded only a
glimpse of Tolkien’s creative process, and many additional sketches,
coloured drawings and maps – although exhibited and published elsewhere –
have never appeared within the pages of The Hobbit.
In
this unique enhanced edition of Tolkien’s enchanting classic tale, the
full panoply of his art is reproduced for the first time, presenting
more than 50 illustrations to accompany Bilbo Baggins on his adventure
‘there and back again’.

ISBN: 9780008627836
For the first time ever, a beautiful slipcased edition of the enchanting prelude to The Lord of the Rings,
illustrated throughout with over 50 sketches, drawings, paintings and
maps by J.R.R. Tolkien himself, with the complete text printed in two
colours and with many bonus features unique to this edition.
Bilbo
Baggins is a hobbit who enjoys a comfortable, unambitious life, rarely
travelling further than the pantry of his hobbit-hole in Bag End. But
his contentment is disturbed when the wizard, Gandalf, and a company of
thirteen dwarves arrive on his doorstep one day to whisk him away on an
unexpected journey ‘there and back again’. They have a plot to raid the
treasure hoard of Smaug the Magnificent, a large and very dangerous
dragon…
Written for J.R.R. Tolkien’s own children, The Hobbit
was published on 21 September 1937. With a beautiful cover design, a
handful of black & white drawings and two maps by the author
himself, the book became an instant success and was reprinted shortly
afterwards with five colour plates.
Tolkien’s own selection of finished paintings and drawings have become inseparable from his text, adorning editions of The Hobbit
for more than 85 years. But the published art has afforded only a
glimpse of Tolkien’s creative process, and many additional sketches,
coloured drawings and maps – although exhibited and published elsewhere –
have never appeared within the pages of The Hobbit.
In
this unique enhanced edition of Tolkien’s enchanting classic tale, the
full panoply of his art is reproduced for the first time, presenting
more than 50 illustrations to accompany Bilbo Baggins on his adventure
‘there and back again’.
Unique to this edition are
two poster-size, fold-out maps revealing all the detail of Thror’s Map
and Wilderland, an illustrated 88-page booklet, and a printed art card
reproducing Tolkien’s original dustjacket painting.
It
is additionally quarterbound in green leather, with raised ribs on the
spine, stamped in three foils on black cloth boards, and housed in a
custom-built clothbound slipcase. The pages are edged in gold and
include a ribbon marker.
The slipcased edition looks pretty much how I'd imagine it, though I was kind of hoping that the page-edging would be done in bronze or copper, as gold was already 'taken' by The Lord of the Rings. That's really the only thing I'm not too happy with, and even then, it's incredibly minor.
If you own The Art of The Hobbit, you have an idea on what to expect, though here are some preview images: (they had to be shrunk a bit to fit within the confines of the blog page)
