I like this proposal the most. We should decide a name of which layer to use as the name for the whole thing in the case of two-layer HF. And then keep the same notation as we use to day for spec docs, e.g. Capella for CL, Shanghai for Engine API specs.
Using a mixed name is a good one but I don’t like it because everyone will have to keep three names in mind when talking about two-layer HF.
Note that we will run out of Devcon city names in case of >1 HF per year. Devcons to be happening in locations defined by EL’s HF names is one of potential solutions to this problem.