I am not sure I completely understand what you are suggesting here.
You are correct in stating a task can be marked complete by pressing the spacebar. I am not sure how this resolves the interface issue of its status indicator being on the opposite side of the screen on a Mac in full screen mode. This would be an expanded view for iOS. An expanded view for a Mac that runs applications in full screen mode, no; or at least one should not be criticized for running OF2 for Mac in such an “expanded” mode. Maybe you consider any task manager to not be able to be properly viewed beyond a specific set of dimensions? It seems to me interface elements from an iOS application should not be expected to work equally well on a Mac application without any modification to their placement (or functionality) in regards to differing screen size.
Right-handed checkboxes work on OF2 for iPhone because the dimensions of the screen are limited; horizontal scanning in this case is minimal. The sole functionality of communicating task status works well for that size of device. Right-handed checkboxes do not work well on OF2 for Mac because the dimension of the screen are larger or “expanded” AND the checkbox is the only interface element which conveys the task’s due soon or overdue status. Thus elements are unnecessarily separated from one another at larger screen dimensions. The placement (and corresponding distance) of the checkbox is an elevated concern on the Mac — specifically because it is the sole element intended to communicate this additional information.
My suggestion here, like I have stated before, would be to revert to OF1 functionality in modification of a task’s text color. This would allow OF2 to maintain checkbox location on the right-hand side for consistency across OmniFocus applications while sharing the communication of task status with additional elements and functionality more suited to the device screen dimensions. The changing of the text color to signify a task’s status as in OF1 resolves the dependance on a single element, the checkbox, to convey this information. The application would more effectively communicate task status without a need to scan across the full screen in identifying specific due soon or overdue states.