I don't think the first part of your argument is strictly true. If you use the @key's option, it would be possible for keys to not exist, or to be added dynamically, thus you might still need to see if that key happened to exist or not.
However, you're correct that none of this stuff helps at all with respect to "auto-vivication". And your code example does appear to help work around the problem when dealing with nested structures.
Hmm, Merlyn recently posted a snippet that walked a structure to it's leaf nodes, maybe we could combine the ideas of that snippet with this code to create a new form of exists?
PS. the last paragraph was written "tongue-in-cheek", but it's late, and I would not be at all surprised to come into work on Monday to find someone actually wrote such a beast...
In reply to Re^3: The Bad, the Ugly, and the Good of autovivification