As an avid new ST fan (due to TMP), I vividly remember the announcement that ST II would feature a young, female Vulcan protege for Spock (and also introduce a young, male, wannabe Kirk) and how Saavik and David would become the new blood of whatever post-ST II life the ST franchise might have. At the time, we knew that it was Paramount's TV arm producing ST II, so we were assuming a new series, or revival of "Phase II", or at least a series of telemovies, and that such an arrangement would give Shatner and Nimoy their "chance to move on" when they were ready. However, the general fan assumption was that Saavik would be a rather flighty "Mary Sue" type, rather like any young female character added to ST fan fic of the day!
In Australia, we had a science fiction media convention in February 1982 and, at that time, "Starlog" had not had anything like the plethora of studio stills they'd had for TMP the same distance out from the US premiere (ST II was destined to open in the US on June 4, 1982, but much later in Sydney). One of the attendees at this con had lots of Japanese connections and she brought with her, hot off the press, a volume of Japanses Super-Visual magazine, which featured several small photos of ST II - our very first glimpses of the new uniforms... and Saavik. Imagine several hundred fans all trying to look at one magazine while the owner held it open.
Our next surprise was an air freighted copy of the Starlog movie magazine special in the June, giving us just enough time to replicate the uniforms for our own premiere night, and of course, Kirstie Alley's voice is the first we hear in ST II. It wasn't anything like we'd imagined and suddenly all concerned that Saavik would be "annoying" dissipated.
The fan buzz around the death of Spock, Nimoy's resistance to do more ST, how Saavik would carry on "Spock's legacy", her appearance as Saavik in Walter Koenig's ST play at the Ultimate Fantasy convention, the rich character backgrounds described and developed further by Vonda McIntyre in the ST II novelization, garnered a lot of support for Kirstie Alley's talents. The thought that a new ST franchise, focusing on romantic leads, Saavik and David - to perpetuate the Kirk & Spock mythos in ways only the slash zines had so far been able to do - were intriguing.
So the recasting (and reimagining) of the Saavik character for ST III took many people by surprise. Suddenly "we can live without Spock because we have this wonderful new character" turned into "Yay! Spock's back! Robin who?" We often wondered if Nimoy had noted the pro-Saavik fan sentiments when he was feeling the yearn to return. And, as director, he was able to have major influence in what unfolded next.