Rob,
Note that the workaround described in the thread you've linked still works fine: use a box, hide the sides save one of the vertical ones, and you can then resize the box as you see fit(thus resizing the vertical line).
I think this limiation is due to the fact that objects in general tends to be resized as if they were boxes, yet the line only has three "dots" that allows you to resize it. So when you rotate it, resizing now works from a rotated perspective, yet since you don't have all 8 dots that you'd have on a box, you end up losing some control.
Even if it was working, however, it would still be easier to simply use a box and hide sides than it would be to work with a rotated line and attempting to resize it correctly. I suppose a real "vertical line" shape could be added, though to be honest, in all the PlanetPress documents that I've seen, there is rarely ever a need for lone vertical lines, and boxes works better for most of the cases. (vertical lines are often just part of bigger boxes, and in the case of columns delimiters, it's usually quicker to use a box since you can make multiple columns at a time, and easily control those columns width) As you mention, it's been 8 years, yet in all those eight years, there has never been an official request for this. So I think it's fair to assume that the need for it is low, and that's probably why they never implemented it.
Regards,
Raphaël Lalonde Lefebvre