Yes, 192.168.1.1 is the most common, but I have also seen 0.1, and 1.254, and sometimes 10.0.0.1 and similar addresses.

Plus, I often change these addresses, which I admit is uncommon, but this approach would let you plug in a laptop to the box and type in the domain and immediately see the address. (You can see it by doing this and then looking at the routing table or DNS server it advertises, but this is more work and beyond many users.)

Having a permanent backdoor address has its downsides, because you can have two boxes on the same network. These days these routers are also the cheapest way to get extra access points -- you leave the WAN port empty. But you still want to be able to get at the control address, in which case you want to change that control address, and disable the DHCP. No real easy answer there if you forget the address because you can no longer get it with DHCP. Broadcast ping has been one way I've managed to do it. I guess the backdoor address approach could work if you temporarily removed it from the network.

But I'm glad people are doing this, I just have not seen it in the boxes I have been using.