Martijn, you are correct. My intent for this thread was to propose #1, but I also mentioned #2, which lives at this thread.
I'm glad you like the idea of #1.
I'm sad you don't like #2. 
Based on the other thread it seems like folks could benefit from it. I'm still not sure what the hangup is with this kind of thing, but I personally am not going to push it since the custom metadata (subject of this thread) would suit us fine.
As to your implementation suggestions, they seem fine to me.
Our users never see the XML so whether we are doing orx:meta whatever or jr:preload whatever, it doesn't matter as long as it works.
I also care about the purity and harmony of the ODK xforms spec, of course, so I'm happy to contribute to that discussion.