Alright everyone, reporting back:
With some guidance from the people at XDA I have fully relocked my bootloader after reinstalling the stock ROM. However, after waiting several minutes after setup and manually checking for updates, I was still unable to get the OTA updates to kick in. I will give it one more shot tomorrow before I send it to electronics recycling, but I am confident this will fail due to the initial bootloader unlock phoning home.
The final alternative for us is to reverse-engineer the OTA update server and make these updates publicly available at our own convenience, which a few people have already started doing. But my own opinion is that we've now hopelessly crossed this line from being enabled by ASUS to do cool things with our phones to being directly at war with ASUS. I don't have the patience to fight a manufacturer with something as mission critical as my smartphone. This is precisely why the moment I knew that ASUS abandoned firmware support for my phone, I moved on to another manufacturer while I try to salvage this phone from ASUS' scam. ASUS has successfully defrauded each of us for several hundreds of dollars and we'll just have to live with it.
I will use my influence to drive everyone I know away from ASUS products and I hope this post sticks around for everyone to read and follow suit. I will also be filing complaints with several consumer advocacies.
