You CAN have one kernel I suppose, though arguably some devices need a different one.
but small Phone, large tablet, desktop primarily with mouse/keys, TV set screen and Server need different GUIs
They need to stop this nonsense (since 1993) of branding everything windows and believing one fits all. For years PDAs / Win CE was crippled by Win95 style GUI. NT family security and integrity damaged after NT3.5
1) NT3.51 gratuitous Office 95 WinAPIs invented to stop win 3.x running office 95
2) NT4.0 unlike explorer preview for NT3.51 integrated too much graphics and printing to Kernel
3) Stupidity of Direct X (so DOS games could be ported
4) Win9x apps on NT4, 2000, XP needing user to be Adminstrator.
5) Aero Stupdity and down grading existing GDI APIs in Vista. Win7 should have been free, only a SP.
6) Stupidity of Win CE/ Win9x reversal of insisting keyboard/Mouse desktop machines should have the Zune inspired interface that only makes sense on small phones On Win 8
7) Win10 is long line of downhill ride since NT 3.5
Perhaps MS will learn and bring out an Enterprise Classic Workstation and Server with best of NT3.5 and XP?
Or will Win 10 be a progressive fail requiring Azure/Cloud and impossible to use without Internet.