By changing the position of a layer (or calling its "moveTo" function) all other layers with a "parallax factor" (a vector) will follow the movement of that layer accordingly.
An alternative way to specify parallaxing but only for orthogonal layers is where it matters that reaching the lower left corner of the map also means that all other layers align with the moving layer. To achieve this, instead of a "parallax factor" one would specify the "scrolling region" of a layer. If that region is smaller than the map's dimensions (in points) then that layer will scroll slower.
This task will require "moveTo" functionality in TKMapNode for scrolling in general, which is going to be a function that takes a velocity vector as input.
Estimation: 3-5 days