Alternate take and apparently unpopular opinion: the US government can simply force Apple to give them a back door to access iCloud photos directly.
What Apple has done here is both way more complicated and way more visible than necessary, while being less useful to a government. The slippery slope and capability to exploit is cloud storage.
I'll add to your alternate take: technology like this starves of oxygen the singular argument (disingenuous as it is) which has proven tractable in the public sphere against robust E2E encryption. With this technology in place, never again will the Government be able to wail "think of the children" when claiming E2E needs a Government sanctioned back door.
What Apple has done here is both way more complicated and way more visible than necessary, while being less useful to a government. The slippery slope and capability to exploit is cloud storage.