Prior to the recent change, everyone working in Japan was a "skilled" worker. There was no language requirement and essentially anyone with a degree was eligible. This didn't cover manual labour jobs etc.
But at the same time, many young people were out working in convenience stores, fast food restaurants etc. Turns out they were all on student visas. With a student visa and a work permission application (essentially a rubber stamp that is never not given) you can work up to 28 hours a week.
So the changes are trying to bring the visa system more in line with what people are actually doing. People without degrees can actually get proper working visas in Japan now.
> "Permanent residents are allowed to apply for Japanese citizenship after five years."
Technically you can apply for citizenship without permanent residence (green card equivalent) though I don't know what your chances would be.... Also you must give up all other citizenships.
> "Some foreigners will also marry Japanese nationals, and their children will thus be citizens as well. Since the new law prevents visa holders from bringing families with them to Japan, many of the new workers will likely be single people looking for spouses, making them more likely to marry locals."
This is true. In fact, by far the fastest route to permanent residence in Japan is marriage. You can get PR in 3 years if you are married to a Japanese national vs 10 years if you aren't.
Previously there were issues with the working conditions for people on the so-called "trainee" visa. One of these conditions (imposed by the workplace) included "No relationships". I hope the new visas don't come with similar stipulations.