That's not what the trial is; workers will be paid 100% of their salary for 80% of their usual time. That's what makes it different from a 'flexible hours' pilot.
Overtime is extremely uncommon even in Europe and has to be agreed upon in contract, and even then most employers just provide extra time off instead of money for full-time workers.
Yes, but eventually that will normalize to a raise if the trial is made permanent, the reason they structure it like that is if they revert that the employees won't see it as a pay cut.
Which is fine. The goal of the trial is to reward employees for increased productivity (historical trends tell an impressive story) by offering them the opportunity to keep their existing salaries by working (and therefore stressing themselves) less.
Sure, high performers should be rewarded using subjective metrics, which is already the case for blue collar workers. This trial gives people the opportunity to not be penalized for working less, which is the case with all the existing flexible hour arrangements. If successful, I have no doubt that this would lead to a longer term bigger change in what counts as full-time employment when it comes to taxation, immigration, and retirement.
It's already a success elsewhere, I really don't see the point of a trial, they should just do it. In NL I don't know all that many people that still have regular 40 hour work weeks, the vast majority are 32, 28, 24 or even 20 hour workweeks, which incidentally helps a lot with leveling the pay gap between men and women.
You interview for a job -- the offer is €X @ 40hrs/wk; you tell the HR that you'd like to only work for 80% of the time since you have childcare responsibilities. HR either writes back that the job requires you to work 40hrs or they revise their offer to €0.8X.
When 80% is the new 100%
You interview, get an offer for €X @ 32hrs/wk; you tell HR that you'd like to work extra since you're really passionate. HR either writes back that you could take extra time off or they revise their offer to €X + conditional bonus of €Y.
Like you said, working more doesn't mean more productivity, and so if a company is paying more just for you sitting in front of your computer more, we're not talking about the same jobs.
And if all of this normalizes, sure, salaries would be rebased, but the negotiation changes, as described above.
Overtime is extremely uncommon even in Europe and has to be agreed upon in contract, and even then most employers just provide extra time off instead of money for full-time workers.