I am aware of exactly 0 ARM motherboard makers that make boards with socketed (read upgradeable) CPUs.
I know they are made for PowerPC. I know there are tons of x86 ones.
For a while I bought motherboards with upgradable CPUs. I quit doing that after a while because by the time I wanted to upgrade, the newer chips required a new socket, I needed faster memory that the motherboard didn't support, etc.
I wasn't aware that it had to be socketed to be open?