Having not long started building a Windows Phone app in XF a number of issues with the back button handling are being hit that are struggle to be addressed.
The back form processing in XF pops the page from the navigation stack which is not always required. The back button is to be used back up user interactions and not just pages.
Consider the following scenarios
1) It is usual for a page to have a base state that the used interacts with to change to a alternate state; e.g. Page One-> Page Two: display state -> page two: partial edit state.
In this this case, pressing the back button should return the user to the display state from the edit state and not return them to Page One, bare in mind there could be a few alternate state and you would want to avoid generating and managing separate pages.
2) The WP message dialog is poor and unattractive, so its typical to design a popup message dialog that mirrors the app theme. Pressing back when the dialog would dismiss the dialog and not the page.
3) Context menus are used frequently in WP, pressing and holding on a list item displays an action context menu. When a context menu is displayed the back button is used to dismiss it without action.
XF needs a mechanism to not auto pop a page when the back button is pressed. Either let the developer explicitly pop a page when a back button event fires, or allow for the pop to be cancelled and another action performed.
This is a potential show stopper for us.