The other problem with this concept is that it isn’t needed as a floating marina provides docks for loading and unloading, stay aboard or go to town. With all the conveniences of a marina, why would we want to reinvent the wheal so to speak?
I like your creativity, and I acknowledge that there may be a need for the system that you are thinking of, even though I don’t see it myself. You are aware that anchoring in the deep ocean is not an attractive option, so we do need another way to hold large platforms in place.
For the Marinea project, this is phase 3 (deep ocean) and we are still working on phase one however, my initial ponderings about the subject required large diesel motors and props in a low current area. We wouldn’t have to run the motors all day just to periodically to re-position. It could even be automated but it is still expensive. A way to reduce the fuel cost would be to grow it ourselves. All oil was algae and grasses at some time in the past. We can make our own, but again, we won’t have to worry about deep sea until we get the shallows under our belt so I’ll just follow along.