It's not so-so, it's a terrible idea. At a minimum, the implementation should cough up keys in (say) reverse order, or some cheap to implement different order than insertion order.

Two years down the line, the amount of code that depends on insertion order will make it impossible to do further optimization.

[Many years ago I wrote a platform with an unintended ordering scheme in its dictionary. The documentation stated in bold that order was not deterministic and could change. Users started reporting "bugs" when I changed the order. That sucked.]