This Rygelon achiev is pretty pointless or I'm missing something?
As for things that are going away this is short list on paper, but meta-achiev for SL require some activities in covenants, meta achievs for ZM, Korthia, Maw, Tazavesh hard mode and last but not least maxing Torghast including unclocking all traits.
EDIT: Btw, "Once the Dragonflight pre-expansion update arrives, all Shadowlands raids will become Fated for the rest of the expansion." Maybe I'm reading too much, but if they keep fated rotation for whole 9.2.5, I think they planned full X cycles through raids. Which makes 25th October pre-patch even more likely.