Ah yes now that I think of it again I think that's what she meant.
I think Kajiura tends to work with people she already knew and established a camaraderie (?) now. When you work with people you're already comfortable with, what you want is easier to get across. Although, that also could be the cause of her songs being stagnant or not as good as they used to be. I have more problem with the songs' melodies than the vocalists, though.
I'm still not into her adding more people to FJ. If she adds a permanent member to FJ then she had to rework the harmonies when they sing lives and while it could potentially be good it could also potentially be disaster or overcrowded. Unless, this new vocalist is a one time singer only. But then again, japanese fans or even us could probably complaint. Say Kajiura composes a new song for FJ X (new). We could probably say, the song will sound better if W/Kaida/Kei/Kao sings it because we're used to their voices. Just remember when she composed Sora wa Takaku for Haruna. We all say that the song will sound better if Keiko sings it, and Haruna isn't even a part of FJ. FJ girls has worked together for more than 7 years and adding more people could disrupt the harmony/the sound they've established as theirs. Hiring new vocalists, yes. New member to FJ, no. That's my stance.
As for the stage presence, I agree with grunty more, the distance between each of them and them to the audiences might play a factor (save for Kaori, which as Kowz said, looked like she'd rather be anywhere than Kajiura lives as shown in vol.11). But that could be because she's way too tired because YKL#11 setlists were way too heavy on her. We don't exactly know how she is in YKL#12 this year. The setlist might play a part as well because for me YKL#11's setlist was really boring, even more than #9.
I don't think Keiko isn't as energetic as she used to be, because she still enjoys jumping around when the song and the audiences set her mood into, as shown in Mezamashi 2015 live. But yes they need to stop singing Ongaku and red moon. I want to say the band also plays an important part because Sato's drumming is sh*t and can't bring the song's energy to the fullest. I mean, YKL#4 is definitely exciting, both to the eyes and the ears because Nozaki was there. Kajiura big 3, mezame, salva nos, and zodiacal sign sounded much better in it :p