AFAIK a standing wave requires the interference of two waves going in opposite direction, as in a resonant cavity. How does that work in a boundless space? Do we need some kind of time symmetry for this to work?
The relativistic effects create this standing wave, i.e. the particle distorts the spacetime as it's moving and the relativistic "glitch" mixed with the modulated ds2 creates the standing wave. IIRC, the idea was to apply the Lorentz moving frame transformation to the ds2 x exp() interval to derive some bits of QM. To derive the non time-dependent SE, some bits of GR were needed and to derive the time-dependent SE, more GR was needed.
Is this glitch the same as what causes an accelerating charged particle to emit photons?
I have no idea. The "glitch" I meant is the Lorentz coordinates transform.