No, I think a line down the middle of a single canvas would just become content - like all the other (freer) marks. The juncture has to be physical - on a par with the stretched canvas surface - to be convincing
form. And the distraction/irritation is vital - these things are about a struggle for perception, breaking things down, putting them together. It has to be tough, uncomfortable.
As for Hockney, I'm at a loss to explain a lot of things there - not just multiple panels!
The artist I mainly think of when I see modern polyptychs of some sort, is James Rosenquist. I think he started doing it for purely pragmatic or practical reasons - the entire works were just too vast to be seen, exhibited or transported on a single surface, and it often coincided with the kind of fragmentation of images he favoured, so works just become
an entire wall or walls of abutting panels Of course, when they get to that size, quite a bit of space is required for the viewer to step back from the thing to see the whole, and you tend to find everyone congregating up against the wall opposite. But when they do step back like this,
the panel's joins all but disappear! (in this example one can just make out the grid of comprising panels - but you have to allow that the work is about 40 feet wide!) It's also a mark (or measure) of the potency of the content Rosenquist deals in.
I've done it in my own work and
there it is just for practical reasons - couldn't afford a canvas/stretcher 8 X 12' or the space to work on it in one go, etc....