The pilot is a team-wide thing. You won't have a 30-hour employee on a 40-hour team. 30-hour employees will work with 30-hour employees under a 30-hour manager. I think that will help offset some of this, but it does put a limit on what projects you could work on. For the pilot, anyway. I'm interested to see how this pans out.
I recognize that 'You won't have a 30-hour employee on a 40-hour team'... my point is that, unless they segregate them in another building, probably another company, the pilot teams will interact with the non-pilot teams... and, at some point in the hierarchy, will be managed by 40-hour people.
As jaded as I sound, I do think there's a place for workplace flexibility. What would really tell me the executives are committed to it: Calculate their actual FTE's - average work week hours divided by 40 - and make sure there are at least that many physical FTE's.
There's no reason why you cannot do that. Our contractors get fixed hour allocations, and often will strictly work to the hours they are paid for (we won't pay overtime without approval).
A few of my folks were angry about this and claimed to be working 50-60 hour weeks. My response was "there's a easy solution to this problem". They cut out the excessive OT, which was mostly unneeded, and not too much changed.
This might be a team wide thing at Amazon but I have seen mixing the two in a single team. Its called reduced hours and can be very helpful for people coming back from maternity leave (as well as others).