Dear Daniel
Reading your essay I could see you have the talent, mental stamina and imagination to discover new physics. The problem of understanding motion is a very interesting one. You promote Barbour's theory which I value for relegating time to an emergant status, but think the SS idea unnecessary theoretical complication. Mach's ideas are very interesting, but there are many ways to interpret them.
Starting from very different premises developed in my 2005 Beautiful Universe Theory on which I based my fqxi essay Fix Physics! . I concluded that motion is the translation of a pattern (a concept you use) in the energy and orientation of dipolar nodes making up a universal lattice. In my theory general relativity becomes very simple, but motion involvs a self-convolution of the pattern not only of the object involved but (a la Mach) the nodes making up the surrounding gravitational field, on to those of the entire universe. For example a force on matter causes the pattern to compress first, and then start moving with its length contracted, 'pushing' the external gravitational node pattern ahead as well. This combines Newtonian SR and GR notions. I attach a figure from the BU paper to explain this qualitatively.
I wish you all success, and urge you to stick close to simple physical concepts - one can easily get too abstract using clever mathematics.
VladimirAttachment #1: 2_BUFIG26.jpg