As some background, this question came from a throwaway exercise by my professor for a reminder of Lagrangian mechanics in a relativistic setting. The original exercise simply gave the Lagrangian and asked us to compute the equation of motion. This piqued my interest since it can be motivated as described in my question.
It would seem at least reasonable to me if the question was closed as duplicate or low-effort, in which case I could supply some more details. But it's surprising for it to be closed as non-mainstream physics. Now of course the Lagrangian is not intended to be a model of some real system, since it's just a toy system that's easy to compute with. Nor am I asking for the correctness of any personal theories. It is instead asking for pointers to literature studying a specific physical system. Should this question be reopened?