The breakthrough here (and I've only skimmed the article) is in 1) reverse osmosis 2) without organics-clogging of filters. That is, basically, keeping pond scum from fouling your molecular-differentiating filter system, which is what it takes to split water from salt.

That and various energy efficiency improvements.

Much of this comes down to questions of "what are the energy costs" and "how much energy can we supply".

I'm not a huge fan of desal generally, especially where it's reliant on fossil-fuel energy. On the other hand, it actually plays into another area I've had some interest in -- seawater-based Fischer-Tropsh fuel synthesis (SFTFS). That's the task of taking seawater, separating carbon from it (mostly in the form of dissolved carbonate and bicarbonate -- the dissolved CO2 fraction is small), and electrolysis to split out hydrogen.

That problem divides into a few parts:

1. Electrolysis of hydrogen. Essentially a solved problem at large scales. Example: nuclear powered submarines replenish their oxygen supply through electrolysis (I'm not sure what they do with the hydrogen resulting). Since water is 89% oxygen by weight, the amount of water you need to process here is small. There's an energy cost (more below).

2. Removing carbonate & bicarbonate from seawater. Here the fraction is far smaller -- a few fractions of a percent by weight. The reason you're looking at seawater is because energetically it's far easier than getting CO2 from air. And yes, seawater is also necessary. The probme here is getting enough water -- you've got to process tremendous volumes.

3. Synthesising hydrocarbons from this (that's the Fischer-Tropsh bit). Fairly well established, and exothermic to boot, so it doesn't cost energy.

4. Energy input. You only get out about 60% of what you put in to split out hydrogen. That normally isn't a very good bargain except for a few useful things about hydrocarbons, below.

The upshot is that desal and SFTFS have a few things in common: taking in gobs of water, purifying that so you don't gum up the works, and applying fairly hefty amounts of energy to it.

What desal offers is a proving ground for developing that seawater handling capability, at scale, and in particular the filtration parts. It would also be possible to combine the processing (though there might be other reasons for not doing so). In theory, you'd ingest seawater, electrolise some of it for hydrogen, capture the carbonate/bicarbonate (which aren't of interest for tapwater), feed your C & H to the FT synthesis process, and continue with the remainder of the water to your desal system.

Why bother making hydrocarbons? Because they're damned useful. Renewable energy has advantages, but it doesn't store or transport well. Synthesized hydrocarbons would be precise (and in fact, more precise) analogs of methane, petrol, kerosene (a/k/a jet fuel), and deisel. For some applications, including standby generation, gas heat, some industrial processes, and powered air and marine transport, they're about the only real viable option. I suspect they may continue to see use in private / passenger transport as well, and possibly rail (electrification is an option, but has challenges). There are industrial processes which also utilise gas and oil feedstocks, notably Haber-Bosh nitrogen fixation (though alternate processes might emerge).

Even if we end up with a small fraction of total energy coming from hydrocarbons (marine and air would be ~12% of the present total), the process could prove quite useful.

Large-scale desal could be a proving ground for related technologies.