The Flintstones (partially found production material for cancelled Seth MacFarlane reboot of animated series; 2013)
From The Lost Media Wiki
In early 2011, Family Guy creator Seth MacFarlane announced he would be reviving The Flintstones, but for a Fox audience, as he was a fan of the original series from the 60's, and that the first episode would air in 2013. Little was known about the project for a while, including if it was still being developed or not. Production of MacFarlane's 2012 film, Ted also made people believe it was cancelled.
When asked about the progress of The Flintstones at a convention to raise awareness about Ted, MacFarlane confirmed that whatever he had complete was shelved because Fox didn't think that a version of The Flintstones for an adult audience wouldn't be appealing to audiences. The plan, and whatever was complete has stayed that way since.