Sweden tested a 30 hour work-week and found it to be too costly. For some professions it just isn't realistic (e.g. supply chain/logistics industry).
For the professions where it is more realistic, maybe give them the option of finishing up the week at 30 hours but don't set a hard cut-off. I've found that the more work-hour freedom people are given, the better quality work ends up getting done.
Being quizzed on specific language syntax during in person interviews when they knew I didn't have much experience in that language was annoying.
Also, any mention of a cover letter was frustrating. I think hiring managers have enough info to decide if a phone interview makes sense with just a resume/Github, especially for a technical role.
Also, having to spend 20+ minutes creating an account with all my personal info just to submit an application stopped me from applying to multiple positions. That time adds up during a job search and makes it extra stressful, not to mention you end up feeling like you just dropped your resume into a black hole where it will never be seen.
For the professions where it is more realistic, maybe give them the option of finishing up the week at 30 hours but don't set a hard cut-off. I've found that the more work-hour freedom people are given, the better quality work ends up getting done.