A lot of these "What Could Have Been" posts are focused on pitches for corporate-owned characters. It's easy to imagine DC Comics or Marvel looking at those and saying, "Yeah, no, it looks great, but that's not the direction we want to go in." But very often creator-owned ideas don't go anywhere either, for many many reasons.
Tony Lee (2000 AD, Doctor Who) shared one of those on Twitter not too long ago: an idea for a pulp space adventure that he and artist Stefano Martino created after they worked together on their DC/Zuda project Where Evils Dare. The main character was named Crash Landing, and Martino's pinup for it evokes a strong Flash Gordon feel. Lee wrote that it was "basically Flash Gordon meets The Rocketeer via Warlord of Mars," but it never happened because Martino was "lured away by Europe."
Since then, Martino has returned to American comics, penciling George R.R. Martin's Doorways for IDW Publishing and even an issue of Dynamite Entertainment's Warlord of Mars, so it would be cool to see if he and Lee could do something like Crash Landing. There's a lamentable lack of pulp space comics these days (Christopher Mills and Gene Gonzales' Perils on Planet X being one of the few I know).