The article says 1W/core is a limitation of maximum optical power density in the fiber itself so if you want to push 240W through, you will need around 240 cores no matter how long or short the cable run is.
Efficient? Going from electrical to laser is at most 30% efficient and then back to electrical is also about 30% efficient at best, which means about 90% of input power turns into heat at either end. Not something you'd want to do unless absolutely necessary. To get your 240W out, you'd need to put about 2.4kW in.
If you want to transmit electrical power and there is no need to be completely electrically isolated in every possible way, use appropriate gauge conductors and Y-delta transformer setups to avoid forming ground loops.
So it may technically be better to find a way to a « big » cable that integrate one or several fiber optic strands (to transport data at 100Gbits/s, scalable to Tbits/s in the future) with one or several copper wires (to dynamically allocate 5W to 240W DC power), with USB-C Thunderbolt 4 (that could be updated to future versions) at each end, and create a data/DC power network with them (which would require Thunderbolt switches, routers,…) instead of using PoE Ethernet cables…
With USB-C wall outlets, you could then plug any USB-C devices (cameras, speakers, laptops,…) without needing an individual power adapter for each of those devices, and have them both DC powered and directly connected to the home network/internet…
Please note that, as of 2023, I am aware that it would likely absolutely not make economic sense yet (largely too expensive compare to other technical solutions), but it would help consolidate the home/office architecture around USB-C connector (which in Europe will be mandatory for many devices starting 2024…)