"These are books that contain interesting inserts or duplications of original material. Books that can be considered interactive works of art or immersion experiences as well as being books. Books that are as much about discovery and mystery as they are about reading. Mainly, I'm hoping to discover new titles that fall under this umbrella when others add to this list."

I think you should check out several of Timothy McSweeney's Quarterly Concerns. It is an approximately quarterly literary journal, but they put a strong emphasis on book design. It might fit what you are talking about.

Notable issues:

#4 - boxed issue. Contains 13 stapled chapbooks and one ~80 drama perfect bound.

#7 - artist's folio cover held together with a large, wide rubber-band. Contains seven stapled chapbooks and two small perfect bound books. (The rubber-bands do not survive. Lack of same should not hurt collectibility.)

#13 - Hardcover 'comics issue'. Dust jacket unfolds to a very large, two-sided poster. This issue also contains two small insert booklets. It is not complete without the insert booklets.

#16 - Hardcover tripartate format (ingenious fold-out cover. Book includes 'deck of cards' story (over-sized cards that tell a story), two perfect bound books, and a "Timothy" comb.

#17- The 'mail issue'. Amazing.

#19 - The 'cigar box issue. Also amazing.

#22 - Hardcover that holds three perfect bound books. These books are secured to the hardcover binding with strong magnets. Easily removed, yet easily replaced.

#23 - Hardcover. Another issue with an extra-large dust jacket that is a two-sided poster when removed and folded open.

#24- Hardcover - amazing z-binding cover design. (Also contains insert / excerpt for Millard Kaufman's "Bowl of Cherries".)

#27 - Slip-case that holds three perfect bound volumes.

#28 - Super-cool 'cased' issue that holds eight illustrated books. (Uses elastic bands to slip all of the books into place.

#33 - The 'newspaper issue'. Super-cool, and rare; very hard to find.

#34 - Two perfect bound books; one slipping into each side of a plastic 'cover / sleeve'.

#35 - Trade paper. Bottom of front and back covers are 'heat sensitive'. At first glance, the art shows that it is raining. Rub the cover to build up heat, and the puddles in the street become a 'pond' with fish. Really cool.

#36 - The 'box head' issue. Very hard to find complete and in good condition. Super-cool, though.

#38 - Trade paper. Available in three cover colors: what I would call an extreme-dark-green, yellow, and red.

#46 - Hardcover. Very unusual 'rubbery finish'. Great graphics, colors, and texture. The cover is as cool as the book.

#47 - Slip-cased. Ten stapled chapbooks slip into the case.

Hi, I added a lot of books. They are not in any particular order. So glad I found your list. I wanted to start a similar one myself & never got around to it. Looking forward to delving into some of the suggestions on the list & checking them out. Thanks.