Two kettles in the UK, closer to three in the US where circuits typically top out at 1800w. I actually looked into the feasibility of installing some 240v circuits in my kitchen and ordering kettles/blenders/etc from Europe...too much work lol.
It's very easy with immersion cooling. The article mentions roughly 20kW of heat per 15U which wouldn't even get anywhere near the 100kW+ for which immersion cooling has been designed.
To even get power into the chip they have to have wires running perpendicular to the board - ordinary traces don't cut it.
This is a really far-out design that isn't appropriate for the mass market at all.