To be historically accurate, comic magazines, digests and novels already existed by the time Kirby moved to DC. Warren had broken significant ground in the magazine format (and not just with horror, but satire magazines such as the art & photo-merging Help! from Kurtzman, etc.), and Marvel had two Spectacular Spider-Man magazines in print in 1968. Kirby's first Jimmy Olsen work was #133 from 10/1970; Gil Kane's Blackmark--one of the earliest, identified graphic novels with a heroic character--was published in January of 1971, but its production obviously predated that by what one would assume was some time. The point being that many sought and achieved creating alternative formats beyond the traditional monthly comic book. It is fair to say Kirby was aware of the innovations spearheaded by others, and wanted to explore that himself.

Kirby wasn't alone in that. Read the interviews Eisner did with various creators collected in Shop Talk and there's a lot of creators from Kirby's generation who envisioned broader horizons in format and distribution for comic material and were constantly stymied and put off by existing publishers who wanted to stick with the tried and true. Some tried to go it on their own-Gil Kane with things like His Name is Savage and Blackmark, Wally Wood with Witzend and the like, and later Eisner himself after he stopped doing PS and focused on creating larger works which helped establish the graphic novel format.

Creators were focused on what was possible, publishers focused on what was profitable.

And, I'll throw this in, and some may find it a hot take (and if it is, this is the right thread for it), but fans becoming creators only made the situation worse because they wanted to make comics like the ones they were fans of including format and characters, so they were willing to stick to those things which made publishers and their desire to stick with what works and what makes money happy and allowed them to put off doing the kind of innovations the veteran creators envisioned and pushed for. Necessity is the mother of invention but as long as publishers had a steady stream of fans cum creators willing to fill the trenches and churn out the same types of stories in the same formats with familiar characters, there was no need driving innovation in the areas of formats and distribution. It was only later, in the 70s and afterwards, when the market was shrinking and profits too, that publishers looked for ways to innovate format and distribution to try to increase profitability because the tried and true wasn't working.

-M

Yeah, much as I'd like to believe that the New Gods and the Eternals would have been a commercial success if Kirby had been able to do everything exactly as he wanted and for as long as he wanted, given the nature of the readership there's no guarantee that would have been the case. Even now there are plenty of readers, both fans and professionals, who see little or nothing of value in those comics and there were probably even more of them back then. I still wish he'd had the opportunity to carry on with those stories, though.

I kind of wish he'd have come back to DC and finished OMAC instead of leaving it on a cliff-hanger (and yes, I'm aware of the fan-made continuation). And if we're pitching stuff like that, I'd have loved to see him do a The Demon graphic novel (though I did enjoy that Matt Wagner mini-series)

The more I study that era and his time at DC, the more I suspect they didn't really value him. They just wanted to get him away from Marvel to hurt their sales. 

This article sheds some light on Jack's return to Marvel -- link