There's an economic incentive to solve this problem.
That's a massive amount of plastic, and any efficient method of harvesting it would have incredible returns.
One of my ideas for dealing with microplastics takes some inspiration from the time in Earth's history when RNA was the most advanced life form.
RNA life forms were strands that would naturally form certain shapes based on their nucleotide sequence, and those shapes would do certain things. To reproduce, a usually identical but sometimes different matching strand would form along the length of the RNA.
I reckon something similar could be done with plastic and bacteria: A bacterial colony is made out of plastic, and the bacteria are capable of melting plastic (not melting their colony due to chemical signatures or something) and their colony is a sheet which has geometry such that it wants to form a certain shape which is conducive to a successful colony; something which easily traps plastic particles and isn't easily eaten.
Due to the colony being a sheet, it can duplicate simply by adding a layer to the sheet that doesn't stick on.
Turning plastic into the basis for a new life form is excellent because:>Oceanic plastic a finite resource, so there's no risk of making anything dominant>Microplastics become macroplastics, which are less dangerous>Life forms don't want to be eaten, so it makes sense to have something we don't want eaten be a life form