There are so many things that are energy intensive and not really economically viable: co2 capture, crypto mining, "green" hydrogen, we could see a world soon where a large scale BESS would have an on-site dummy load that does something useful with that electricity

The problem with all those things is that they are ridiculously capital intensive to set up, and then they sit idle 80% of the time Worse, the whole point of negative electricity prices is that they're an inefficiency in the market which ideally will eventually be optimized away. Then what do you do with your billion-dollar plant that can only run with negative prices that no longer exist?

You're assuming the way they get optimized away isn't by these sorts of plants.

I guess the problem with building a pure energy waster is that it could only operate every now and then, and it's not guaranteed to see negative prices in a few years from now. So, might not be all that profitable.

Use the electricity to heat up a lump of iron to a very high temperature, than use electromagnets to fling it into space?

If you heat up iron to very high temperature (>770°C), it's much harder to fling it using electromagnets.

Ah that's annoying. Fine, we use the electricity to heat...uh...molten salt encased in stone, and to pull back a very big heat-proof slingshot, and after a threshold it lets go and launches it into space.

Obviously the complaint is about the changing atmospheric absorption properties as a side effect of the generation side, not the heat from using the power.

Either way I think people are overthinking it though.