Cement buoys are nothing new, well cement ships have been done for at least a 100 hundred years. the Wikipedia below has some info and the video below shows the durability after 98 years of being a wreck.
https://en.wikipedia.org/wiki/Concrete_ship
As the Ceto are stationary and only have to contain a generator (PTO) rather than goods they'll have more than enough space and concerns around concrete ships aren't relevant.
Concrete is an interesting idea - I guess that once the forms are produced they could continually smash them out - concrete is a lot cheaper than steel but concrete reinforced vs outright steel would be interesting. I am sure there are engineers that have rates for concrete, reo and sheet steel. The lifespan of concrete vs steel too could be attractive. as you build it once and leave rather than repaint as you would with steel... Weight could be a concern as heavier barges/ tugs would needed to haul them to site... I guess that's why they are doing the feasibility study.
A eco advantage of concrete could be artificial reef situations where you make holes for fish.. obviously biomass aggregation would have to be considered unless they clean them from time to time which would defeat the point of them being colonized by organisms.
Email catalyst and other shows like 60minutes etc. I'm sure that there is a good enough story that it could warrant a story. They won't generally do stories unless prompted to by the public.
https://www.9now.com.au/60-minutes/2018/extras/latest/send-a-story/60-minutes-send-in
