This is obviously not the case. If every node on the network swaps to a dark themed GUI, nothing changes for anyone else. If every node on the network swaps from opt-in to full RBF, then a lot of things change for a lot of businesses and entities.
But that's my point. It's a nothing feature. It's not part of the protocol so it's meaningless. It should be a checkbox in the UI.
I really don't understand how there could be so much debate over a feature that ISN'T EVEN PART OF BITCOIN.
If anything this debate just demonstrates that Bitcoin development is a monoculture.
Someone should release a "jailbroken" version of Bitcoin Core that allows you to have your node behave in any way you want.