The reverse is solved with a single button activating the default qwerty layout?
The direct with family is similar - you can have an extra layout installed
So the leaves even fewer cases where you really have to switch (but unfortunately not 0, no easy mechanisms to just easily switch to a some downloadable layout named after you on the fly at any computer)
Then there's the reverse: My PC at home - wife wants to check something quickly without turning on her PC.
Finally: I regularly use both a PC and a laptop. Depending on how weird you want the layout to get, there may not be a way to use it on the laptop. Schlepping an external keyboard around - nope, not practical.