Understood.
For the scope I am bringing up, we use 10 or 20' lines to layout utility structures for construction along with other misc items. The lines are entered perpendicular/radial/parallel to the controlling feature, elevated to the lowest invert, and named per the structure name. When the field tech selects the line for layout, he's presented with the name of the structure and cut to lowest invert for labeling the stake. There are many ways to skin a cat but we found this method to be easy and flexible.
The intent of the request was so that the name assigned to lines, along with the elevation via the line marking toggle, can be quickly visually checked for accuracy and content before sending to the field. Once everything checked out, the layer containing the name labels would be turned off in all likelihood. Currently, quality control would be all I would be looking to do with the feature. But given the ability, I'm sure other uses would surface.
For the example above, they would all be single segment lines only. As they are relativity short, a single label at the center would probably be ideal. What I envisioned was, selecting all the lines by layer, calling for the line name field, and BAM! all the structure names can be verified visually by only panning the project opposed to panning around and individually selecting each line (sometime several hundred) and verifying via the properties panel.
I can't speak for your other users but, I am currently at a loss as to why there would be the need to display name labels on multi-segment lines. Especially contours and the like. But again, given the ability, who knows what your crafty uses will come up with.
I don't feel like I've helped and answered your questions as I'm pretty much narrowly focused on my needs verses the big picture that you need to consider. However, I hope my long winded post is of some help. I'm starting to feel like this may be a candidate for the new _TML feature. But to find the time to figure that out..............
Rich