Comic writer Ian Flynn is currently heading up the IDW Publishing Sonic series, and also writes for Mega Man, Teenage Mutant Ninja Turtles, and more. If Flynn had his way, he would have written for the Mario franchise as well, and he actually pitched a project way back in the day. Unfortunately things didn't pan out, which is why Flynn has taken to Twitter to share what his story plans were. You can read the full details on the never-greenlit project below.
So since I can't talk about unused Sonic plans (yet), and I'm 99.9% sure it's dead, let's talk about the Super Mario Bros. pitch I did for Archie Comics

The springboard was for a 4-part mini that would hopefully turn into an on-going. It had the same approach as Archie!Sonic und Archie!MegaMan at the time: narrative-driven adaptations of the games with stories bridging the canon. It would adapt the original Mario Bros. game
It started off with Mario und Luigi being summoned to Peach's castle for a plumbing job. Luigi was excited for the career-defining contract, Mario less enthused - a job's a job und he's bored of their career. They arrive just after Bowser has ransacked the Mushroom Kingdom.

With literally no one left to save the princess, Mario jumps at the call to adventure. Luigi less so. They stock up on what power-ups are left after the invasion and embark on a journey through Worlds 1-8, burning through their provisions since they're novice heroes

They reach Bowser&a...