When that is the case, we will have largely addressed climate change already.
Using a "surplus" of base load carbon sources to run compressors is just pushing sand into sand.
Without the climate crisis, doing this R&D only once the technology becomes required and therefore economically feasible would be fine. But with the current decarbonization targets, you cannot just build renewables until you hit a threshold, and only then start testing out storage methods while putting the green energy infrastructure industry into hibernation for 20 years. We pretty much need to do everything, right now, at the same time.
This is also why there is a big economic advantage of hydrogen storage. Decarbonizing steel and ammonia production with blue hydrogen (i.e. electrolysis using electricity created with the current fossil fuel heavy generation mix) is already a big potential market which is already kind of feasible, reducing the need for government subsidies to get the tech off the ground.
Once the R&D, production and sales pipelines for blue hydrogen are up-and-running, you just scale up with increasingly mature technology. Then transition the energy input from carbon-intensive to carbon-neutral. This should happen automatically, as green electricity is the cheapest form of energy, and the hydrogen production acts as an energy-sink for any surplus production, mitigating those adverse market pressures acting on renewables after you reach a certain percentage threshold on renewable energy generation. Only then you eventually ramp up the use as energy storage via normal market mechanisms.
Unfortunately the media always seems to put the cart before the horse. Energy storage is not the first step, but should be the last.
My house is grid negative from about 11:00 to 19:00 with about 2 months of engineer salary in battery and solar.
It seems like the first and only step available to anyone outside of massive power tycoons, and if I repeat the investment for just a couple more years, it is also the last step.
I think the media reports on anything clickable, but also probably hopium technologies endorsed by energy tycoons to facilitate kicking the can.
Unfortunately, there is not enough (economically extractable) Lithium to go around. Experts estimate a Lithium "hole" of up to 300.000 tons of missing yearly production by 2030.
There is nothing we can do about it, only prospecting for more Lithium, reducing red tape for Lithium mining (with all the negative environmental impacts), or further increasing efficiency of Lithium use in batteries. As you said, Lithium battery technology is mature, so we have hit diminishing returns here.
This is why the feasibility of sodium batteries that was announced a year or so ago was such a big deal. Getting Sodium (e.g. from table salt, mined as excess in potassium mines, with a price of around zero) is easy and cheap.