The plot of Ant-Man and the Wasp was all about coming to the rescue of Janet Van Dyne, but apparently, her character could have turned out very differently. While the Janet we met in the newest MCU movie was a kind person whose first act back in reality is to help somebody trying to hurt her, it seems that there were early conversations that, had things gone differently, could have made Janet Van Dyne the villain of the film. Ant-Man and the Wasp director Peyton Reed was recently asked about the speculation that Janet could become a bad guy in the future and he revealed that the possibility had already been discussed at the beginning. According to Reed...
I can say that it was certainly one of the things that we talked about.
The idea of the original Wasp being the bad guy isn't that crazy an idea. She's been stuck in the Quantum Realm for decades at this point in the Marvel Cinematic Universe. She's had no human contact in that time. It's entirely conceivable she could have gone mad in that period. Either that, or she's simply become furious for being left there for so long and wants revenge on people for not finding a way to get her out.
Even the version of Ant-Man and the Wasp that we saw, which focused on Ghost as the, somewhat sympathetic, villain of the piece, could have seen Janet Van Dyne go in a very different direction. When she put her hands on Ghost in order to infuse her with energy that helped heal her, I honestly thought she might fry the girl's brain or otherwise use the quantum energy to destroy her. It didn't end up going that way, but it could have.
With Peyton Reed admitting that discussions took place which saw Janet Van Dyne as a villain, it makes one wonder what the future might hold. The original question from CBR wondered if Janet could become a villain down the road, and if the idea was considered once, it certainly could be again.
It would make for an interesting idea. Seeing heroes become villains is a classic trope in comic books but it's not something we've seen in the MCU yet. We've seen "good" people turned evil through various means, but never a character that had been previously well established as a hero. It's likely a matter of time before that happens. Michelle Pfeiffer would probably make for a fantastic comic book supervillain.
There almost certainly will be more to the story of Janet Van Dyne in the future of the MCU. Exactly what happened to her in the Quantum Realm and what the long-term consequences of that are was barely dealt with in Ant-Man and the Wasp. It seems quite likely this will make for an important storyline in some future MCU film. The only question is what it means for the character of the original Wasp.