I like to timestamp a lot as I draft, so I find the “Insert Date” shortcut for Windows really valuable. A similar command in the iOS version (especially if invokable as a hardware keyboard shortcut) would be a great help.
The trouble with this sort of thing is that there is very little room in iOS to place lots of smaller insertion features such as this. On macOS and Windows you have the menus, which can then be associated with keyboard shortcuts, and the menus are easily discoverable by users. There is no equivalent on iOS. The nearest is popovers, and they are not suited to added lots and lots of different features.
So the only way I can see adding an “Insert Date” feature is as a keyboard shortcut (which is easy enough), which would then only be available for those with external keyboards. (I suppose it could also be added to the keyboard accessory row.)