Have a unified protocol for this doesn't mean a monopoly or consolidation.
Look up the implementation of UPI in India.
We have thousands of services providing UPI payments to any other UPI recipient (no matter which app they use as long as it supports UPI)
Even WhatsApp has a UPI payment button in India. It's that easy to implement.
I might be terribly oversimplifying it (and deviating from the facts a bit), but think of it as email - a protocol - and the thousands of services that let you send/recv emails to anyone, no matter their domain or service.
All the grids have even number of squares (equal black and white).
Therefore it is impossible to start on white and end on white while covering everything else.
I don't have the formal proof for this, but can be proven with examples. In each of your grids.
I'll be following this thread to see if someone shares the formal proof for this, fingers crossed!
Doesn't quite roll off the tongue as much (ironic lol)