"The NIPs repo is a record of consensus among implementations."
That's great, but if the protocol doesn't prescribe anything, then it's not really a protocol.
Discussion
Once the group defining a protocol arrives at a consensus, it must be clearly defined and fixed in order for others to participate.
If any part of the protocol specification can change when the consensus shifts, then it's not a protocol, it's a developer clique. Anyone outside of the group that defines the specification will be left in the lurch with incompatible code.
I know nothing about coding, but this makes a lot of sense to me.
The NIP repo prescribes a lot of things. Basically everything. It's just dynamic is all.