Why?

"Price for Bitcoin is too high, no power for your home today, unless you outbid the market"

You're choosing to consider the case when the price is very high, but not when it's very low. The flip-side of that coin would be that energy not worth being put into mining, which would be sold at a loss to the grid, would instead be put into batteries and saved, to be sold when when market prices were high again.

But I think by the time Bitcoin becomes so universal that all energy companies are mining companies, it is likely to already be at the scale of USD/EUR, or even become the reserve currency of the world, in which case it would not fluctuate nearly as much as it does now.

Yes, I'm choosing the case where the price is too high, because most people rely on energy being available and that's why there's a number of laws (depending on the country) that protect from disconnection. In practical terms, I prefer my freezer not to stop working and spoil stored food rather than having universal world currency which fluctates less.

Then we shouldn't have an issue, since I explained how such a system would continue to provide in that case.

Why would anyone run an energy storage system for general population in that system? If they can undercut the energy companies at some times and sell to the Bitcoin miners, why would they even bother with residential customers?

Sure, people who can afford energy storage themselves would be sorted. (Most of the time) Anyone below that wealth threshold would be at the mercy of "am I more important than the monetary gain today".

Because it would be profitable, that's how markets work.

It could be profitable. But miners will buy energy as long as the price is lower than the expected return, regardless if it comes from excess renewable or from storage, do it may be more profitable not to. This means a bidding market between the miners and tenants for the stored energy. And that's not the uncertainty I want to live with every day. (Because that market is no longer realistically possible to regulate given the energy producers become the bank, the mint, and the business running them)

Do you really think that Bitcoin, the first prototype of a decentralized currency, will be the primary electronic currency ever? We've only just begun exploring the design space, and it's terribly arrogant to believe that we'll be stuck with this prototype even just 20 years down the line.

I don't think there's anything particularly arrogant about it. My ego doesn't depend on Bitcoin's success. You could say that expecting it to still be around then is naïvité, maybe. But of course, I still disagree.

Bitcoin's success has more to do with its monetary policy and hard-money aspects than with the way it consumes energy. Monetary policy isn't something we've seen any innovation with at all in the crypto space. Different coins have different inflation curves, but inflation curves exist in all currencies. They're not a new concept, they've just got specific variants.

But also, Bitcoin isn't static. It's still being developed. And I think its focus on slow stability and payments makes it more attractive, not less, in the long-term.

It's already been here 11 years, 20 is not so many more. I fully expect it to still be around then, and almost certainly in the top position in crypto, if not globally among all currencies.

If you can't see why it would be a bad idea to attach the price of electricity to a speculation-based crypto coin, or how the prospect of mining bitcoin would be a joke in nearly every location on Earth except a few small regions that happen to have just the right conditions, I'm sorry but you're beyond salvation brainwashed in your cult.