That is an interesting idea. I guess you could probably set that up somehow. Although I’m not sure if you can necessarily access that data live from your electricity company. I imagine you could probably just accomplish the same thing by running at 3am every night.

I’ve thought the same. But quite anti-social for apartment dwellers

Depends on the building. The last two apartment buildings I lived in, you could hardly ever hear anything at all from neighbours. One was in a century old building, one was in a completely new building a couple of years back. YMMV.

But how would that work in practice?

You load the machine say in the afternoon/evening after work etc, and then it decides based on historical data that 02:35 is the local minima and starts. You run the quick 1-hour program because it's Good Enough(tm), then the laundry lies wet in the machine from 03:45 until you wake up around 06:00 to start your day hanging it? In my experience, but perhaps this is just local circumstance (climate etc) you can't leave damp laundry in the machine for hours on end, it will get smelly and need to be re-washed.

Also, not being able to plan when you deal with the wet laundry because of the power price hunting feature sounds super annoying and stressful. Perhaps there's an assumption that after the laundry it will also tumble dry; we rarely do that due to it being bad for the clothes and costly in energy etc.

In Europe spot prices are announced 24 hours in advance so it's actually very easy to this. It's super handy for things like battery-electric vehicles or central heating. For the latter you also take in the weather forecast into your model, and voila, lower power usage, better comfort. For BEV you can easily set plans to charge it even more than usual to take advantage of unusual drops.

My washer and heat-pump dryer don't really use that much electricity. They've become super efficient. There are better and lower hanging fruits than such appliances these days.

There is a ripe for socket power relay that you can configure when should the power come on based on electricity spot price.

I've often wondered why no new manufacturer has appeared with a stacked system that can wash clothes in a top washer and then dump them into a bottom dryer, or even an all-in-one frontloader.

Front-loaded machines with both a washer and heat-pump dryer exists. I've had one for many years. It's quite handy if you have light loads, but I much prefer having a stack of separate washer and dryer, even though it means I have to manually move them from one to the other.

You know I had the vague thought of searching to see if they were actually out there but dismissed it as unlikely (at least in NA) because I've recently been appliance shopping and never saw one in person.

Combo washer/driers exist. They typically have less capacity than stand-alone units.

Drying performance is shit. Especially since you can pack a washing-machine fairly full without affecting performance, but a tumble-dryer needs to be loosely filled. But even so, the combo machines don't dry well.

Probably because that would much more mechanically complex and therefore expensive and failure-prone, and the market has decided that the existing options are good enough (I'm not defending this, just describing what I see).

Miele already offer this on newer washing machine. They can connect to your inverter too and start a load when there is available local solar/battery/low spot prices.

It’s called “SmartStart”

It works very well in my experience. Load the machine in the morning, and it will start later in the day, then send my phone a notification when the load is done