It would definitely cause complications, but if it's economically sustainable, shouldn't incentivizing additional hiring be a societal goal? Not only would it reduce unemployment, it would improve work-life balance.
The article didn't provide details, but I'm imagining if workers are capped at four day workweeks, but businesses still operate five to seven days a week, then you can get more coverage without burnout.
Certainly there would be overhead of not just more people to train and coordination between people operating on different four day windows, but frankly, what is management being paid to do if not figure out problems such as this? Already you hear about sectors from medicine to law to investment banking where despite earning high salaries, workers are forced to endure ridiculously long hours and deal with high stress. Why not spread the workload?
Reminds me of job-sharing proposals.