A dev switch on current Chromebooks enables Developer Mode easily. The developer switch enables the command line shell. The switch is behind a little door on the right-hand side of the chromebook.
However, a physical dev switch may not be present on at least some of the upcoming Chromebooks.
Here is a commit message on Chrome OS I noted today.
factory_Finalize: Fix the checking of dev switch
factory_Finalize will first check if there is a physical dev switch
through crossystem vdat_flags.
The task check_developer_switch will only be added to queue if there is a
physical dev switch.
TEST=Run finalize test on snow, link,
there will be no check_developer_switch task.
Run finalize test on lumpy, there will be check_developer_switch task.
Lumpy here is the Samsung S5 550 Chromebook and Snow is an upcoming Chrome OS device. So, Snow will not have a physical dev switch. Will it include an option to enable dev mode from settings menu? May be, we can not be 100% sure at this point. Will all future Chrome OS devices come without dev switch? That is not sure as well.
We will have to wait till Google releases Daisy and Snow