I haven't been waiting for a timeline as long as you have, but I've been waiting 18 months. That is even too long.
I haven't verbally asked questions for a couple of months now because we never seem to have enough time, or it's not the right time and often he can't remember anyway.
I totally get your frustration. I made the timeline one of my requirements for R and I still don't have it although FWH thinks that we are nicely along in R.
So, what I did, was email him many questions in a time sequence, that if/when he answers them, will construct the needed timeline.
I also said that when he feels that my needs are important enough, he will sit down and think hard and answer them. He assured me that he does think that my needs are important and he actually devoted one evening to answering the first two questions.
He says it is a work in progress. We'll see when/if he continues.
One way I described my need was that I needed to sort out all the clutter in my brain. The information I have has come from me asking certain questions. I wonder what information exists that I haven't thought to ask for. That actually was one of my questions.
In writing them down, it helps to select those which are really important to you.
Try it and give him a deadline.