A couple things, and to be clear I'm really narrowly focused on appliances/ immobile applications. I don't think these heavier batteries are quite yet ready for things like phones, drones, scooters, EV's.

I think specifically this battery technology addresses your issues directly.

Firstly, there are actual reasons why current battery technologies are not allowed to be used in specific indoor applications, and that is thermal runaway (effectively your third criticism). Generally, LiPO's are not legally allowed for use in permanently installed indoor environments. The reason why is thermal runaway.

Here is a video of an idiot puncturing a lipo cell: https://www.youtube.com/watch?v=yzBFCufUDq0

Here is a video of an idiot puncturing a sodium cell: https://www.youtube.com/watch?v=W1ya_ls1zkA

Spot the difference? Its the fire. The only reason we don't currently have LiPO's acting as stores of power for current technology is that you DO NOT WANT lithium fires to happen indoors. A sodium battery will explode (see idiot A). But it will not catch fire and will not create a thermal runaway situation.

Secondarily, appliances are already heavy. Adding weight for something like a battery isn't an issue because you don't need to move the thing very often. The amount of additional design complexity is small, and something we've basically already solved in so many ways. We don't need the portability we would need for a vehicle or cell phone.

Thirdly, I think the complexity is trivial. Complexity hasn't stopped producers from adding what amounts to a small computer to everything from a refrigerator to a tea kettle where literally a simple switch would do.

Easily rectified by adding a physical cutoff.