I came close to ditching ranks (and also considered only having white and black). Here's what I would have done; it's theoretical, but I think it answers some of what you're contemplating. I'd have changed absolutely nothing about my curriculum, except formal testing. I'd have taught things in the same order I have them in, held onto stuff until an individual student's skill and competence made it a reasonable thing to teach, etc. The tests would still be there...just not as tests (nearly all my tests are really similar to drills I use, so I can get that information from the drills). Just no ranks.
Of course, that removes things like earned seniority (based on rank), so I'd probably ditch some of the formalities and just have everyone bow in (same ritual) without regard to seniority. And I'd have just determined what constitutes "good enough" to be ready to learn to teach (which, incidentally, would probably be the same criteria I use now).
My program is (and likely always will be) small, so rank doesn't serve as much of a function as it could in a large MA school. Some of this might be more complicated in that larger-school context.