I think this will definitely occur. In the same way that organisms could not work with wood fiber's lignin during the carboniferous period, we're seeing it play out in a plastic period of our own construction. The Earth will win, but whether we will see that happen depends on all of us.

Maybe eventually https://science.sciencemag.org/content/351/6278/1196

Probably not soon enough to help all the creatures that don't benefit from ingesting plastic.

It happened with things like lignin after their evolution in the carboniferous, but it took hundreds of millions of years. In the meantime we got a significant fraction of the Earth's fossil fuels as indigestible plant fibers were deposited and turned into rock.

We're in the early anthropocene. After a few hundred million years there might be bacteria eating away at plastic waste in the abandoned basement layers of the cybernetic hybrid post-human/AI city-organism that covers most of the planet. DNA importation from off-world organisms exposed to cosmic rays might help.

In the meantime there will be layers of anthropocene-specific minerals deposited just as the carboniferous left its own unique signature.

There actually is such an organism, but it only breaks down PET. (aka polyester, which is the 4th most common type of plastic) https://www.sciencealert.com/new-plastic-munching-bacteria-c...

I wonder what potential by-products of said organism would be. ex. gases released

Already happening. There's a bacterium that's already good at living in the interface between the aluminum foil and plastic in a CD.

But we can't count on it to undo the damage within our lifetimes.