Plug your own router? Sure, put the BGW320 into passthrough mode and 3rd party NAT works fine. You get the public IP on your device and there is no double-NAT. The broken bit is, regardless where you NAT, you still run into the 8,192 session table limit of the device anyways. The only way around that is via unofficial means (which is part of the $20 to just not deal with ATT. The hardware could damn well do passthrough without that limitation). At least that's something you can workaround to a true fix though as opposed to no IPv6, where your best bet is tunnel somewhere.
You grab your own 10G-PON ONT box like the Azores WAG-D20 which lets you set the MAC and ONT values to the same as the ATT one. Works pretty good, only complaint I have is there aren't any "ONT on a stick" (i.e. SFP+ module ONTs) that let you do that last part so it's still a box with a separate power supply adapter.
Their FTTN stuff definitely would only work with a router that somehow managed to break third party NAT, even in when running in its bypass mode.
(Out of 7 ISPs at over a dozen sites, this is the only time I have had this issue. Support couldn’t diagnose the issue.)