Here is the current transitions between different modes:
Toggle Live Preview/Source mode
Toggle reading view
from/to
live preview
source
reading
live preview
1
2
source
1
2
reading
Transitions from reading mode depend earlier editing mode used. The earlier editing mode is determined by two factors: tab specific editing mode and in case of new tabs default editing mode setting. The problem is that the user should remember whether the tab was new or which editing mode was previously used. This problem occurs only when transitioning from reading mode to source/live preview. In that case we could have two additional shortcuts:
The first link below shows another feature request with three commands which allows you to switch directly to any mode of your choice. These can then be assigned to three different hotkeys.
The following thread shows an option to cycle through all three modes with just one command.
Finally here are some other related featute reequests: