TL;DR
Effectively Being Able to drag signals along a track, where they place along the track once they reach the given train length. Similar to how poles do so for max length between poles.What ?
Say you have a track signaled for 10 car trains, and you want to re signal for something smaller or bigger, Your two avenues right now are either manually going section by section, signal by signal, or blueprinting a section, then having to remove all the signals that are there, and then blueprint and place. The idea Is being able to assign a length, say 2 cars, and being able to click and drag like poles, the signals will only place so its two cars between signals.A bonus would be to auto deconstruct/mark for such any non matching signals