Andrej Karpathy discussed this a bit in the AI day presentation, mostly as a future state of affairs. It's an understandable concept and kind of exciting to think that the car will be familiar with all roads as long as a few Tesla drivers have been there before.
So I'm fully on board with the concept and looking forward to its realization. However, so far I think there is little evidence that oft-driven routes are making their way into the NN, encoded in the gigantic matrices of weighting coefficients. Certainly we see the FSD beta testers encountering the same route, intersection and lane confusions, release after release, with some improvements but also with fresh pathologies. Even the much-discussed California-rich training advantage is not clearly evident regarding routes and lanes - it comes probably more from a better understanding of California style road design and markings.
At the other end of the spectrum are the North Carolina test videos put out by Rocco Speranza. Compared to California, NC is a nearly Tesla-free zone and there are many unfortunate errors of planning, routing and understanding. For a while he's been chalking those up largely to navigation-map problems and I think that's right.
One other note - when it does happen, I think it still is not within the definition of "HD Maps". Those are specifically centimeter-resolution databases and include an enormous amount of labeled objects, road paintings and everything that doesn't normally move. When the NN-memory map does arrive, it it won't be a so-called HD map, but a huge collection of "I've been here" memory engrams (a great word I learned as a kid by watching the original Star Trek series, long before artificial brains were anything close to achievable).
Here's a very relevant, entertaining and classic song from that same era, this cover by the great Johnny Cash (done earlier by Hank Snow, and there's a great UK version). This is how Tesla will hopefully be in a few years: