prepare a wall for plumber and piping
It is not uncommon for folks to install &quot;access hatches&quot; in areas that commonly have problems (e.g. shower valves) but I don't see any reason for access in the spot you reference. The in-wall plumbing for your new toilet is no different than all the other plumbing in your walls that is covered up with drywall.
Access hatches are always visible (and not usually pleasing aesthetically) and creating one is more work than just repairing the drywall. I don't see the point.