A new Microsoft-branded Bluetooth accessory has passed through the Bluetooth SIG. The Microsoft Modern Keyboard was listed on the 31st March 2017 and supports Bluetooth 4.2.
It may be the same device as the Microsoft C3K1780 keyboard which has jut received FCC certification on the 9th March 2017, in which case the keyboard appears to be a wireless desktop model like the Surface Studio keyboard with likely a full set of keys including a numeric keypad. According to that documentation, the keyboard also included a convenient USB wired mode, and it appears to use a rechargeable battery rather than AA cells.
The keyboard may be revealed at Microsoft’s long rumoured but somewhat uncertain “Spring” hardware event with the new Surface Pro 5, just confirmed by Chinese certification authorities.