Invincible will be creating more original plotlines for the TV show as we head into future seasons. The creator of the comic series, Robert Kirkman, has confirmed as much, saying that the show creating original content is something that's "fun and exciting to do."
"Any lack of new storylines in the television show is not due to a death of ideas from the writers. The writers on the show have tons of ideas, and so, yeah, you can expect more side quests and things that will be working their way into the overall narrative of the show as we go on," Kirkman confirmed in an interview with The Direct.
Co-showrunner Simon Racioppa said that for original plotlines to work, they can't feel like they're filler content. "It just needs to feel organic to the show, right? Like, the big thing for us is there shouldn't be any episode you can skip," he said. "Every episode, we only get eight of them a year, eight of them a season. Every episode has to move Mark's story forward, has to be important. You shouldn't be able to remove anything. So, that's one of the contents. We might have a great idea for an episode, but if it doesn't fit into the storyline, if it doesn't illuminate some aspect of Mark's character, help him mature, take him to a place he hasn't been to before, that still plays into the whole season, then it can be a great idea, but it's a great idea for something else."
Currently, the Season 4 episode in which Mark travels to hell with Damien Darkblood is the show's lowest-rated episode on IMDb. There's always the chance that new original content could make a better impression, but it's clearly a gamble with the pre-existing fanbase.