In what I am pretty sure is a first from IDW Publishing and their MLP Comic line, the My Little Pony: Art Gallery II—which was solicited way back in July of 2015—has been officially canceled by IDW Publishing.
After months of the Diamond Distributors constantly pushing back the release date (this book was originally scheduled to come out in October of 2015) the release date eventually stopped on April 28, 2016. Date came and went with no book materializing. The official confirmation of the cancellation is listed in the PreviewsWorld Cancellation Archive for May 2016 (search for Item Code: AUG150408) with a number "4" present after the title of the product.
The number "4" is part of Diamond's Code for identifying the reason why a particular item isn't coming out. A number "4" means that the item has been canceled by the publisher—which in this case means IDW Publishing.
While this is technically new to the MLP Comic line—I can only think of two instances where variant covers for two different stores were created and not used due to the comic store dropping the exclusive comic covers—products get canceled by comic companies all the time for a multitude of reasons. Just take a look through the PreviewsWorld Cancellation Archive (which goes back to 2009) for proof of that.
Interesting to note is that Art Gallery II is featured in My Little Pony: Art is Magic—which came out in the month the Art Gallery was originally scheduled for release.
Twitter: The Illustrious Q