Motivation
If users want to select a revision by clicking, the current UI forces them to click on the slider line. This may be quite slow, as the right spot to click has to be found first. Furthermore, when users search for a revision by passing over the bars and reading the tooltips, they sometimes drift away from the clickable area, which is annoying when you found your revision, want to click, and can't (anymore).
These issues would be solved, if the area above the slider (i.e. the bars) were clickable itself.
Task
Make the area above/below the slider line clickable, where it is clear what will happen. This means: Everything below the yellow slider is clickable for yellow, everything above the blue slider is clickable for the blue revision. All other areas are still not clickable.
To indicate the user what will be happening, highlight the half of the column where the pointer is situated in the color of the knob that would go there. Also, add a "ghost" knob to the slider, as shown in the mock:
