For as much progress we have made on land our capabilities in subsea engineering are still very limited.

I work for one of the world's premier subsea firms, we do the vast majority of our work for the oil industry. The many factors involved with working deep underwater make it a monumental effort to design, manufacture, install, and maintain equipment on the sea bed. Even then we are just using it as an interface between the surface and reservoirs contained beneath the seabed. Each installation is around the size of a house at the well and then miles of risers and flowlines.

To perform any sort of large-scale ocean cleanup would require accessing the 70% of the Earth's which is under the sea. This can only be done with massive leaps forward in subsea robotics technology to produce equipment to accomplish this task without destroying the seabed. It would be the most massive engineering project in human history. We are still at least a century away in my opinion although I hope I am wrong.