There's a bigger story hidden behind the achievements of memory champions. The groundbreaking result from the past few decades is not that there is a way for a human to memorize a thousand numbers, or that a particular method of memorization (say, memory palace) is the way to do it. It's nice, but not that relevant for everyday life and not applicable to most life problems.

The true achievement is recognition and verification, across many disciplines, that: 1) there are better and worse ways to improve skill 2) anyone can improve any skill [if they do it the right way] 3) mental representations are key to high performance. Some are better than others. 4) one should study how to learn a given skill, or get someone who knows that to teach, e.g. to study people who are best at something - to find out their training regimen, their way of structuring the information/skill/work/memory/... - this is likely to work everywhere 5) If that doesn't help, i.e. little progress is made, one can still figure out, discover, create their own ways of practice to advance. 6) the upper limit of skill is way way higher thank we think 7) Many fields don't have clear criteria for success, so little feedback is available on low-level performance details, which limits the progress of training methods.

If you're interested in all that, I recommend reading the book of a renowned scientist who actually discovered a lot of this stuff and who worked with early memory champions, provoking them to push the boundaries of what was thought possible -- Anders Ericsson, "Peak: Secrets from New Science of Expertise".