Yeah, that's the bit that makes me think there will be a shitload of people cut off from vehicle ownership by the electric revolution.

It's time to end that stupid suburban sprawl, and make places walkable, cyclable, and have subsidised public transport. Because when the petrol age comes to an end, those people left out of the new one will revolt.

Sometimes, but not often. These are mostly 1st gen EV batteries, so they're pretty old. It's mentioned in the article that once capacity diminishes to the point of effecting range the old battery is replaced. Old units can be refurbished. These units could also be situations where the car surrounding the battery failed (accident, hail damage, etc) and they decided to scrap it and reclaim the battery.

At one time, they didn't last more than a few years, and needed expensive replacement. Newer batteries have better BMS controllers on them and last a lot longer. But any damage pretty much necessitates replacement. The batteries can probably be fixed but IDK if they can be put back into use in vehicles then. So there's plenty of used batteries that can be upgraded to use for stationary storage. You can buy them all day long on certain websites or auctions. It's a pretty popular thing for DIY solar.

When they've reached end of life for the car, they are still useful.

EVs require high energy density so they get replaced when they don't store enough energy for their weight. However for grid storage, weight doesn't really matter (at least not as much) so a battery with 80% of its original capacity is a good (and cheap) solution.

When the market is mature, it will good for car owners who need to replace their batteries because the old one still has value.

Think of it like phone batteries, you dont, but overtime, the wear level of the battery is lower than new, and if that range is less than what you need to dailu drive, then people will get their battery swapped.

Its one of the reasons why car companies were hesitent to make lithium ion batteries for EVs

This should make it less expensive if EV owners can sell their old batteries to be turned into a grid battery.

The article mentions that they mostly use batteries from the Nissan Leaf and Honda Clarity. I'm not sure about the latter, but the Nissan Leaf does not have any kind of battery management system. That keeps the battery warm in winter and cool in summer, and helps it last a lot longer. Nearly every major EV on the market does this, but the Leaf is the big exception. It's also the one car where you'll see severe range degradation on an older model.

Sure... at roughly the same rate and/or lifespan as someone with a combustion powered car might need to rebuild their engine or transmission. It's really not that big of a deal, and newer battery chemistries like the current LiFePO packs are continually getting longer and longer lived. BEV battery packs are already expected to last 10 to 20 years.