This seems like a feature a lot people are looking for. I wonder how they'd go about implementing the idea though? I mean, sometimes one needs the straight line done in pencil, other times oil brush, and sometimes even glitter. In Photoshop, the line tool creates just a straight solid line. To get the same effect in PS, one has to use something like the Pen Tool to map points on a path, then use the "Stroke" path option to outline the path with a particular brush (and then you have the full brush stroke appear, where in ArtRage the ruler could mask one edge if needed).
For me, there are pros and cons to the "Line Tool" idea, so I hope they don't do away with the ruler altogether.
Nothing is easy to the unwilling.