... could you show me any published code (CPAN module, etc., even obfu will do) that uses the lvalueness properties of a flattened hash?

Unfortunately, no code that uses the lvalueness properties of a flattened hash comes to mind. I think this is due to the fact that values and slices provide both lvalues and a list that is at longest half the length of just %h.

Would you rely on this in your own code?

In all truth, no. This is mainlydue to the fact that I would use values or slices instead.

Also, please note, the point of my OP is not about arguing that Perl should do this or that

If I came across as argumentative, I apologize.

To conclude, your opinion falls into for the sake of consistency, right?

Somewhere in there. I think it's behaving somewhat like a list of scalars with every "odd" one (as you put it) an unmodifiable value that doesn't die when you attempt to modify it. If that qualifies as "for consistency" then yes. I cannot think of a reason why you wouldn't offer it when the facilities for it are available. Furthermore, aliasing the values is less expensive than copying to a read-only list.