Didn't had much time lately... This is what I have till now, and I apologize sincerely for the code; it is ugly, undocumented and very little tested.
About the lisp. It takes every perpendicular and tangent direction or every curve that pass thru dimension's definition points, plus horizontal, vertical and aligned orientation (in current UCS). After playing a little bit, I found it very annoying when are too much objects and/or very close orientations.
Try to select a common intersection of at least 3 lines and you'll see what I'm talking about...
But I really like the opportunity to have horizontal, vertical and aligned dimension in one command. I've done a "light" version including just these options and I've already replaced dimlinear command on my autocad. I can tell you, I am extremely delighted about it.
That's all for now, though there are still many things to fix, but it's not gonna happen too soon, at least not me.