The first one that comes to mind...and maybe there is already something like this and I ain't found it yet, is the object equivalent of text to path. In other words, take an object, or series of objects, and repeat it, either oriented "perpendicular" to the path at a given point (ala the text function), or oriented as it is to start, but repeated along the path. Either one with a user specified interval.
Next would be perhaps some kind of sine wave function, with options for wavelength, amplitude, and various types of distortion, i.e. sawtooth (if you want to reverse it, just flip the object in the opposite direction), square wave, and "clipping" of the wave. It might also be possible to use a second wave to "cut" sections of the first wave or amplify them...not really sure what could be done with such a thing, but it might be useful. It also might be interesting to make the gradient tool work in conjunction with this "wave" tool, you could specify whether the gradient would start at the center of the wave's amplitude and fade in/out toward the center/edges. Maybe all of the above is possible with existing functions somehow or other...I am pretty new to Inkscape and have just begun to explore it's possibilites.
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