Gusuku Etymologies

Histories of the Ryukyu Archipelago refer a lot to important sites called gusuku, a term whose etymology is the subject of much disagreement. Here is a an admirably open-minded summary from Wikipedia:

There is no consensus about the etymology of gusuku. [Basil Hall] Chamberlain analyzed the word as the combination of gu (< honorific go 御) and shuku (宿). Kanazawa Shōzaburō also segmented gusuku into gu and suku but considered that the latter half was cognate with Old Japanese shiki, in which ki was a loan from Old Korean. Iha Fuyū proposed that suku was cognate with soko (塞, fortress). Hirata Tsugumasa considered that suku was cognate with Japanese soko (底, bottom). Similarly, Higashionna Kanjun raised doubts over the analysis of gu since older records always used honorific u (< o) instead of gu (< go). Nakahara Zenchū identified gu as go (stone).