I have to wonder how much of the delay is due to Elon wandering back into the FSD lab where all the programmers are working furiously and making some grand pronouncement that stops progress in its tracks, like "We're going to move to a vision-only system! Get cracking! No more radar!"
(Yeah, but this is how it plays out in my head...)
There are many very technical videos on YouTube about the details of Tesla FSD, typically presentations by whoever's the head of the team at the time, or leads a particular sub-project. There was one by a guy on all the work they did the bring vision results for determining distance and velocity of objects up to the precision they'd previously had with radar. They've apparently done it, but it wasn't easy, and watching the presentation I kept thinking "Why didn't they just stick with radar? How much did re-architecting the system for vision-only nuke the schedule?"