The main risk I see is things getting shipped overseas to where it isn't properly handled and this policy not having any effect at all.

If that can be avoided somehow (I haven't looked in detail at the legal text) I think the outcome you mention would be good. Slower fashion cycles, higher quality and higher cost per item would all potentially synergise. Another thing that could happen is less overproduction, which would also be good.

Thinking about what else could be done: I would like to see some mandatory marking indicating fiber / weaving quality. I have had T-shirts that lasted a decade, and those that lasted a couple of years. And it is very hard to tell up front which is which. As a consumer I would like to be able to tell.