Don't know if it's going to be a wholesale take on "It's a Wonderful Life"(which is a case where I actually enjoy parodies better then the original, as I found it be a forgettable movie, hell it only got popular in the first place due to constant reruns in the 70s) or if that's only going to be part of the plot. Either way i'm intrigued.
Here's how I think the plot might go: Bikini Bottom is having a big anniversary celebration with the Krusty Krab doing the catering, Spongebob suspects Plankton is going to attempt to steal the formula at the event, but in his attempts to stop Plankton he ends up ruining the celebration, resulting in the entire town getting pissed at him. While aimlessly roaming around depressed, Spongebob runs into the Flying Dutchman, who decides to show him what life would've been like without him ever having existed. This turns out to be part of Plankton's plan(turns out the Dutchman is the one person who actually likes Plankton's chum, so he bribed the Dutchman with his entire supply of it to get him to do his bidding) as with Spongebob busy (and Krabs too distracted bemoaning the loss of money over the ruined celebration) Plankton now has the perfect opportunity to steal the formula. Meanwhile Spongebob discovers that in the future life would be much worse without him-Plankton is the ruler of Bikini Bottom(which has become a futuristic dystopia ala Blade Runner) and all of Sponge's friends are slaves to him. Spongebob then gets stranded in the future and has to fight to help the rebellion overthrow Plankton and also find a way back to the present, after doing so Spongebob decides not to go through with wishing himself out of existence, the Dutchman then lets it slip that it was Plankton's idea, so Spongebob then has to stop Plankton's latest plan(which involves finally building the Mega Bucket) form coming to fruition and win back the town's approval.
Yeah I could see that, could make for a great movie.