Note that I did include a stopping point in the sketch to avoid "overpushing" the Jolla when opening the keyboard. I am not really concerned about it though, the main use would be the slide channel to guide and force straight push.

What I am concerned about, however, is accidental but dramatic risk of fall of the Jolla when open. Even with strong magnets, a force applied perpendicularly on the Jolla (either screen side or battey side) would detach it. Force would need to be strong enough of course, but that can happen very easily when you are using your phone in a crowded area (subway for instance), but also in many other situations.

So, to avoid that, what would be better than the previous pic would be a sliding mechanism like in the pic below:



It would still be very easy to remove the keypad: just open it and go beyond the "open" magnets. The stopping point is on the other end: you can't go beyond the "closed" state. Doing the opposite (putting the stopping point on the other end) would work too, but I am not sure it would be as secure.

Another idea, close to Sid21177's one, is to use metal bars in the base, in between the pairs of L and R magnets. The keypad's magnets would stick to the base's ones in binary positions, and in between (when moving), they will tend to follow the metal bars. I am not sure magnet bars would be needed (plus you would need the same magnetic pole running the length of the bar, whereas poles are most likely on both ends with magnet bars; not sure I'm clear). However that would be less secure than a "hard" system in the plastic as above, and no end point. But more minamistic, aesthetically.