So basically you mean, when the "use cornered paths" is unchecked when placing paths on a grid, it should just round off the placed path and let the attaching paths run over into those empty corners? - I'm not sure if it can do that, I'm also not sure if it would mess with any existing builds.
But yes, nice idea. I see it being useful. - OR, perhaps it could "auto-fill" with something else in those corners, but it might not be as elegant.