The OP is not asking about fixtures mounted to a box. You are suggesting it is against code to loop from fixture to fixture? When installing rows of fluorescent strips in a warehouse each fixture must have a separate fixture whip? How about standard recessed lights in a dwelling? Each fixture must have a separate cable from the switch?
In residential wiring, this is the reason that a device in a box must get its ground connection from a pigtail rather than via direct connection of two ground wires to a common screw on the device.
The case of a luminaire such as you describe is more difficult to accommodate in that you would be removing not just a connected device but a section of the raceway.
In the case of luminaires, that would seem to mean that a ground wire must go from one device to the second one downstream, bypassing the intermediate luminaire, in a leap-frog fashion.
One way of doing this would be to run a conduit the length of the run and, as you suggest, connect each fixture whip to that conduit for grounding rather than relying on the luminaire itself or a ground wire which runs inside the luminaire.
But the context of 250.148, wiring within a box, ("fed from
the box") seems to keep it from applying to this situation. When you completely remove one luminaire, you are also removing the power feed to downstream luminaires, so the ground continuity would seem to be moot.
