The Verge reports that Microsoft may well be looking to relax its requirements regarding the hardware capacitive buttons on Windows Phones. Currently, OEM partners include three buttons on the front of each device; back, home and search. These have been with the platform since launch back in 2010, but we could well be seeing a slight change with potential hybrid hardware and more when Windows Phone 8.1 is released.
Previous rumours had Microsoft removing the back button functionality altogether. So why would manufacturers want to remove the capacitive buttons, in favour of on-screen solutions? To save costs. This will affect low-end hardware (or devices where the hardware buttons aren't suitable), but the main point is the experience won't seemingly be affected by the change. It's believed the virtual buttons will be a black bar at the bottom of the screen.
Sources familiar with Microsoft plans say the company is experimenting with on-screen buttons to ensure apps that have been built around the back button will continue to function as normal. We can look at how Google has implemented a similar solution in Android. Should this hardware requirement be altered, it will signal yet another change to urge OEMs to create low-cost devices.
Finally, The Verge notes that any future hardware specification changes will be related to Microsoft's efforts to have HTC install Windows Phone on its Android hardware. With virtual buttons for both operating systems, it would be easier to manage and deploy said hardware, while cutting cost.
Source: The Verge