SUMMARY It kinda becomes problem when on touchscreen only device if by accident you disable virtual keyboard. It makes no sense to enable/disable virtual-keyboard on phone/tablet devices. you always want virtual keyboard Linux/KDE Plasma: git master
Wouldn't it make more sense to filter it out in the UI. On a dynamic system such as a yoga convertible it would be wrong to hide it and KWin cannot distinguish between a phone and a convertible.
KWin have information about input systems available (i.e touchscreen or tablet or keyboard0, so in my opinion it would make sense from KWin side to dynamically hide/show SNI. Beside filtering out this specific SNI from for example system tray would require very specific code from what I understand.