It's a good idea to submit your feature requests directly to Adobe via their official Feature Request and Bug Report Submission form:
In the meantime, you should be able to accomplish similar results by choosing Select All (⌘A), then Modify > Transform > Flip Horizontal or Flip Vertical. The caveat is, if an element is locked within the Layers panel, it will not be selected and therefore won't be transformed. (By contrast, the Modify > Canvas commands automatically unlock all elements.)
I suspect one of the reasons why these commands do not currently appear is that flipping the canvas itself would not produce a change in its appearance. It's the objects on the canvas that you want to flip horizontally or vertically.
Ah, I hadn't considered States! Be sure to mention that in your feature request, if you submit one. It's a good point.
That said, you should be able to get around this by choosing Show All States from the onion-skinning menu at the lower left of the States panel. (Within that same menu, be sure to check that Multi-State Editing is also enabled.) Then when you choose Select All, it will in fact select all visible and unlocked elements across all states.
(Notice that I'm adding "visible" to the criteria for object selection; I forgot to include that before.)
I also forgot to consider Pages; however, it looks like pages are designed to maintain a high degree of independence from one another. All the Modify > Canvas commands apply to a single, currently selected page only.