I assume and hope that they do not, if there is no rule stating that they are invalid. There are valid reasons for JSON to massive keys. A simple one: depending on the programming language and libraries used, an unordered array ["a","b","c"] might be better mapped as a dictionary {"a":1,"b":1,"c":1}. Now all of your keys are semantically values, and any limit imposed on keys only makes sense if the same limit is also imposed on values.
No part of what you wrote before this in any way suggests anything about the intentions.