So there are no batteries to develop an actual industry around, most are just one-offs.
Nissan's early Leafs have the reputation as the cars with the most degraded batteries coming back into the used car market, and some of Nissan's earliest Leafs were sold under a "battery leasing model" where the car was sold but the battery was still under lease from Nissan giving Nissan incentive to replace the battery if it dropped below certain warranty thresholds. Yet despite the "notorious degraded Leaf battery" and decades of the Leafs existence and batteries that possibly owners could call in lease terms for replacements out there, statistics show that the vast majority of Leaf batteries are still in primary usage (people are still driving those "degraded" batteries, there is a used car market for them) and Nissan claims they've yet to see enough batteries enter the secondary use market to build even a single one of their PowerWall-equivalent products.
People massively over-estimate the range they think they need because they don't take things like home charging into account.
From a regular European 230V outlet you can get 100km of range every night easily. Even more if you don't work 16 hour days.
The average commute around here is a bit over 50km a day, both ways combined.
Right now, hobbyists. There's high demand for used Leaf modules - so much so that they're getting fairly difficult to find these days. Golf cart conversions are popular and easy.
This is a problem the market is perfectly capable of solving. Batteries are valuable.
And the people who bought a 25% worn battery for storage would be looking for another new one at some point, at which time they will sell the old one off for recycling.
I’m not saying it couldn’t be true, but I’m quite skeptical…