Interesting little tidbit direct from Billy Sherwood today, from the Progressive Ears website (at the end of this thread, which is a Yes year-in-review thing).
It sounds like the original intent was for for Squire to be ousted, with Billy Sherwood taking his place as bassist. After some reconciliation or something, Sherwood did some production work for Yes on the Keys to Ascension material, and then became a full fledged band member afterwards.
The plan to dump Squire is interesting, though.