If both mining and non-mining nodes must manually (subjectively) adjust their criteria for block acceptance, what impetus is there for the network to stabilize to any sort of objective state?
Getting back to your question, I have no idea if the scaling functions will stabilize on a singular chain or not. However, I think it would be a Pareto improvement over the status quo. Indeed, you could embed BTC and ETH into DCC (with the proviso that all users must use the core-developer-chosen hash functions and scaling functions), and both chains could live side-by-side.