Keep divided edge straight when dragging it's end point I don't know how to really describe this so I hope it'll make sense.
What I am trying to find out is how do I make vertices, that are dividing an edge, move with the edge as if it was whole and the vertices weren't even there, by draggin the end vertex of that edge.

To give you a simplified example with just three vertices I made these screenshots:



I know that I could just dissolve the vertex and divide the edge again after the transform, but this is just a simple example and I want to do this for an already detailed mesh. Proportional editing isn't optimal either for this, I tried.

As an another example, I saw someone do this in this video: https://www.youtube.com/watch?v=e2EU-alJa-Q&amp;t=3m16s at around 3:16. See how the middle edge loop moves along with the lower edge loop scale as if it weren't there? That's what I am looking for basically.
You may not be able to move other than the active one the way you want by dragging, but you might get closer to what you want to achieve, by using, in addition to the grab tool—G, the rotate tool—R, and the scale tool—S. If I were wanting to do what you want, I'd select all three vertices, with the grab tool, and move the active vertex to where you want it to end up. Then I'd use the rotate tool to adjust the location of the end vertex furthest from the active vertex, so that it is located on a line from the the new location of the active vertex and the location at which you want the furthest vertex to line up. Then, I'd use the scale too to actually set the location of the furthest vertex. 

Note that in doing it this way, it is important to select the vertices in the correct order. First select the vertex furthest from the vertex you want to be the active vertex, then select any intermediate vertices, and finally select what you want to be the active vertex. 

Also, if precise placement of the intermediate vertices is desired, I sometimes find it useful to count the number of intermediate vertices, delete them, place the two endpoints, create the edge, and then subdivide the edge into the required number of vertices. If there is other geometry incorporating those intermediate vertices, sometimes I don't delete them, but rather merge them into the intermediate vertices of the edge I created and subdivided.