Exactly this. Few phones allow bootloader unlock let alone open drivers that can be brought forward to a mainline kernel.

The article seems to refer to a 2023 Pixel Fold as one of their candidates - I guess a good opportunity if those fragile screens get damaged but not a cheap used device otherwise.

Even normal slab pixel devices have limited support for true android replacements like PostmarketOS let alone cheaper 3rd party devices usually running Mediatek/Exnos SOC that have zero open docs or support.