Kryptos : K1. What is the origin of the "palimpsest" keyword?
It was never determined how to derive the keyword PALIMPSEST from the sculpture or its text. It was, as you stated, found by brute-force hill-climbing algorithms.

One theory is that crib-dragging the morse phrase SHADOW FORCES reveals IMPS at SHAD, and working form there retrieving the entire keyword, but I find this far-fetched and implausible.

The keyword for K2 can be found by crib dragging morse phrases, but for K1 it´s still a mystery.