You also need a buttload of electric power, which is the bottleneck.

Not really, my old microwave has 500 Watts, this should be also enough for slow resistive cooking while being insulated.You will find 12V/24V 2.8L/5L Dc Electric Pressures Cookers with 250W-300W on AliExpress. (1l needs roughly 0.1kwh of energy to go from 20 to 100°C) Additionally, you might save a lot of energy by using a hay box after it starts to boil. https://en.wikipedia.org/wiki/Haybox

IMO 500 watts of sustained electrical power is a fair bit, especially compared to every other electric device these households are likely to have.

500wh battery can deliver that for 1 hour.

slow cooking: see above on changing the taste of food that's deeply rooted in tradition

So? Everyone used to cook over woodfire. If the benefits are good enough, like massiv time saving, it will change.