Bug 470519

SUMMARY

Currently when you'd like to change the shell, e. g. from Plasma Wayland to Big Screen, you need to log out, select the shell, enter your password and log back in.

If you use different accounts for each shell, that makes sense. 
However if you use the same account, IMO things could be sped up:

The user selects in some interface to which shell they want to switch and Plasma would do everything automatically:

1) Save the session
2) Logout (is this even necessary?) respectively shut down the shell
3) Log back in (if a logout was necessary) and start the new shell 
4) Restore the session

That way if you switch from your computer or laptop screen to a TV, you could quickly enter the Big Screen shell (whose session gets restored) and when disconnecting from the TV, you could quickly enter the usual Plasma Shell again (whose session gets then restored).