I think there are two factors interlacing: producers' demands (based on the show and their understanding of "Kajiura sound" they brought Yuki in for) and Yuki's own aspirations, preferations and vision of what music befits the show. How much they interlace, how much freedom leave, how much creativeness and urge to do new things they cause - it all differs from project to project, I assume. Bad news is, what WE want is NOWHERE among these factors.
you can always "give up and approach her from afar", or you can write some kind of petition, though I believe the only surefire algorythm is to become a big producer in Japan oneself, launch an animu, lure Yuki in and tell her in person with all the weight of the words one's authority entitles to: "More of this, less of that, try something fresh here, and don't even DREAM of using that Kaori/Wakana combo in the OP this time".
Otherwise, we can only trust Yuki in what she does, hope for new tracks to hook us and rant/grunt/yawn/nod in mild approval about those that didn't. I guess that's what any fandom's fate is about, huh?
Although as natural as it is, I do admit I still have two issues with the complaints around our community:
1) demanding a new trend COUPLED with ruling out old ones (a.k.a. "mo more Emily/Hikaru/Wakana/Tokyo Konsei/flute/eerie sfx/insert something that bores you here"
2) being seemingly less than wary of the possibility that a fresh pattern/arrangement/vocalist may not be exactly to one's liking (see: In Your Eyes, Clara Kennedy, Haruna Luna... Yep, Moonfesta, too, if I may recall Kazado's reaction
).
That aside, I come to realize we're pretty much an ordinary fandom.
Concerning style-abundant OSTs, I agree with George, though I must add that there are always RHH OSTs to show off Yuki's ability in that field, and Madoka OSTs are comparatively motley enough, too, if to a lesser extent. That's regardless of the tracks themselves appealing to anyone or using fresh or familiar recipes.
Of course, one can't eternally ignore the fact that her creative force is not a perpetuum mobile (something she
herself acknowledged). And yet, hope and trust (or give up and stop caring, for that matter) is pretty much all we can do when we expect new surprises to come. Actually, the general vector of Yuki's music seemed to change every four years or so, as far as I can observe, so maybe this year IS holding some aces up its sleeve for us? Or maybe better luck next year? Or later? Only time will tell. Just - I feel like saying it again - be prepared to face even those surprises that may NOT be your cup of tea, lol.