One can only hope that eventually a solution will be developed that fixes the long-lived problems that plastics cause- perhaps a bacteria or chemical that breaks them down. In the meantime plastic waste is here to stay.
Also, robots. But mostly we just need to get off our asses and pick up some trash!
On many of the islands I visited, people did make a conscientious effort to throw their plastic garbage in bins and do the right thing. And that worked great, up until one of the massive deluges of rain that the area gets would come. And since they had no landfill area that was far enough from the water, the rains would wash the entire landfills out to sea in a massive river of plastic waste. It was one of the most depressing sights I've ever seen. On one of the scuba dives I went on, we found ourselves surfacing in a debris field that had washed out to sea and it was astonishing to see the magnitude of it. Collecting everything together, as in your suggestion, just led to a massive batch dump into the ocean and it didn't do anything to keep the waste out of the ocean.
What we really need is a way to simply produce less plastic products. Increased use of glass, increased emphasis on reusing what plastic we do have and, yes, new technology to replace plastics with materials that break down faster so that when they do end up in the oceans, which in much of the world is inevitable from the moment of creation, they don't cause the amount of damage that plastics do.
While there's a lot of plastic in the ocean it's relatively thinly distributed. It's not like there's a bunch of bottles floating in one place. It's a bunch of plastic dust in the water column. Any sort of bacteria or chemical that is self sustaining enough to be dropped in the ocean and expected to clean up the plastic would likely wreak havoc on all sorts of things. Any sort of bacteria or chemical that is sensitive enough that it won't wreak havoc in the environments where we don't want it to likely can't be applied in a effective or economical manner in the oceans.
I do think we have a responsibility as self-aware beings to pick up after ourselves, but at the same time the Earth will be fine long-term. You could even say it's fine now. Yes, species are going extinct at an alarming rate, but we came from the Earth too and are not the only contributing factors to Earth's various disasters. I'm not about to throw trash out the window because of that fact, it's just that I don't have so much anxiety about totally destroying the planet. Maybe we will destroy the planet inasmuch as we can't live on it anymore, but that's our own damn fault and it's almost nothing compared to the longevity of the Earth.
But it's distributed over a very large area, and affects sea-life. Guess what that means for people who consume fish?
Besides the particles' danger to wildlife, on the microscopic level the floating debris can absorb organic pollutants from seawater, including PCBs, DDT, and PAHs.[40] Aside from toxic effects,[41] when ingested, some of these are mistaken by the endocrine system as estradiol, causing hormone disruption in the affected animal.[38] These toxin-containing plastic pieces are also eaten by jellyfish, which are then eaten by fish. Many of these fish are then consumed by humans, resulting in their ingestion of toxic chemicals.[42] While eating their normal sources of food, plastic ingestion can be unavoidable or the animal may mistake the plastic as a food source.[43][44][45][46][47]
Marine plastics also facilitate the spread of invasive species that attach to floating plastic in one region and drift long distances to colonize other ecosystems.[15] Research has shown that this plastic marine debris affects at least 267 species worldwide.[48]
Great Pacific garbage patch: https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch
In people, fails to degrade, in sanitary sewer, fails to degrade, back into the ocean, etc.
But actually plastic slowly degrading at the magnitute it is at, make the small particles spread all over. Probably gives people cancer.
Plastic breaks down into smaller plastic which becomes embedded in biological tissue.
Given sufficient time evolution makes pretty much any waste a resource. Oxygen used to be a toxic pollutant. Then nature evolved and started using it to produce energy in cells.