I don’t think this is a very hypothetical scenario. There are two main players when it comes to governance - the decision makers (core devs / client creators) and the enforcers (miners).
It’s been observed time and time again that the majority of enforcers are either apathetic to governance changes, or purposefully side with core dev decisions. I personally believe it’s apathy, but until we have signals for yes/no/abstain AND “no vote”, it’s hard to support that argument. For those who are not apathetic, there is a strong financial incentive to follow core dev decisions due to a number of reasons.
So, if we assume the enforcers are always going to side with the decision makers, then there is really only a single governance entity (although it itself is not a single body). Still, this entity is comprised of a narrow slice of users/developers that do not really reflect the demographic using Ethereum.
This group of core devs / client creators inhrently have a meritocracy though, like @jpitts is saying. They don’t need even an informal system to determine who is consistently presenting logical discussions and valuable research. I don’t think it’s a stretch to say that people like Vitalik rank quite high on this totem pole, while an anonymous redditor probably ranks fairly low (regardless of arguments being presented). This is the “rough consensus” that was not accidental, but planned from the start.
To an outsider though, it certainly looks and behaves like a benevolent oligarchy.