Can someone break down some numbers here for me? What kind of voltage do you need to move that distance? Will this create huge magnetic fields along the cable under the ocean? (Yes I know almost nothing about electricity :)
I assume the use high voltage direct current (HVDC) power transmission using coaxial cables. Then the electric and magnetic fields are confined between the inner and outer conductors. The outer conductor basically acts as a shield that prevents electrical fields to escape. The magnetic fields also cancel out each other.
Basslink is a fairly run-of-the-mill HVDC interconnector by world standards at 500 MW and 370 km.
The longest undersea interconnector currently under construction is the North Sea Link between the UK and Norway (700 km, 1400 MW): https://en.wikipedia.org/wiki/North_Sea_Link
At 3700 km, Australia-ASEAN would be far beyond the length of anything that has been built or considered to date!
And Australia already has experience [1] of building that type of link.
And according to your link, Australia's Basslink is owned by the government of Singapore. So that helps explain why they aren't afraid to do this. They've done it before.
I remember a lot of these hig voltage technology needs as insulator sulfurhexaflorid. Unfortunately the most potent greenhouse gas, so lets hope leackage is not too high.
https://en.m.wikipedia.org/wiki/Sulfur_hexafluoride
