The reality check is that it's the political third rail in this country to allow for an expectation that's not delivered when it comes to the immigration of parents and grandparents.
Rather than kicking the ball down the road and hoping that this thing self-fixes in a number of years, just be honest and transparent. Just say in the first week of January, or whenever, that we're going to take in 4,000 cases—representing 8,000 persons—because we're going to reduce 12,000 from inventory.
Until you get rid of the chicken and the python, the inventory of parent and grandparent cases, you will never have predictable processing times.
That's the key. Don't take in more files in a year than you can process in a year. To do that you have to cut inventory.