My electric kettle is mostly gathering dust but I decidedly know people who'll boil water in the kettle before putting it into a pot (e.g. for pasta or potatoes). Doesn't make much sense economically if you're cooking with gas and gas is half the price of electricity but does speed up things especially in small households.
Anyway, I could definitely see the additional introduction of 240 V in US household and strongly suspect cheap imported 230 V appliances would eventually mostly replace 120 V versions. A simple switchover to 230 V at distribution level seems more or less impossible nowadays and would likely cause a nightmare of cheap transformers as people continue using their old equipment - plus some damaged stuff as people plug in things using just an adaptor or old NEMA 5-15 sockets are left in place during the conversion.
Polarisation would be pointless with 240 V provided by a typical US 120/240 V transformer since both poles are 120 V to earth. And yes, IMO with asymmetrical supplies polarisation is vastly overrated. I think modern toasters have double-pole switches anyway and even Chinese hammer drills do. Edison base lights are an issue but Germans and other users of Schuko plugs seem to survive just fine with some common sense and unplugging floor/table lamps when in doubt. Some inline switches are double pole too but not all of them.
Double isolation and its implementation is highly interesting! I've never seen double-isolated fridges or toasters in Europe, yet hairdryers have been required to be double-isolated here for half a century!
