Datacarriersize is currently, as of Core v29, 83B and it can be set to any other value. Sadly there is no way to just ask nodes about that setting, right? I'd love to see if people use the setting to increase or decrease the value currently. Guess, nodes could track transactions they receive and from where they got them to defer that setting over time but did anybody do that? To limit the datacarriersize to 40B as Knots, you can just use Core v29 with that setting. Running Knots is really a form of protest and not the expression of a datacarriersize preference. That said, I don't see clear evidence for "a significant portion of the network even changed proactively their node implementation" as the numbers we see at coindance are easily and cheaply faked.