The USPS already partners with all the big carriers for Amazon deliveries, so they could solve the problem.
Alternatively: put in boxes not owned by the usps, and use combination locks. The "special delivery instructions" box on every order form on earth already supports this.
The main problems with outdoor lock boxes are moisture and heat. The main problem with indoor ones is that you need a mail room, and they tend to be shared.
I don't see how this new product helps in most circumstances. I guess it could be useful in high crime urban settings, but mail lock boxes are already common there.
How would that work with multiple delivery services? A FedEx or UPS worker, for instance, cannot legally put a package locker key into a USPS mailbox (and usually, in apartment mailbox banks, cannot even physically do so even if they are willing to ignore the law).