Honestly, I'm getting bored by all these Keiko discussions there and there, everywhere. Find it disrespectful for the two other girls and Yuki Kajiura. Kalafina is Keiko for sure, but also and equally Hikaru and Wakana, each one having her "role" in the band, as assigned by Yuki Kajiura, because she thinks that's for the better, and we can't do anything to change that, period. Kalafina as a whole, as for the voice part, globally sounds fine like this, there's quite a balance between the two girls - it can't be perfect, for sure, but you can't say that Keiko is obviously left behind - and I can't see any reason for this to change.
Kajiura-san hired her for her ability to sing with a deep voice, there's no reason to ask her to do something else, nor to ask Kajiura-san to write her songs especially to give Keiko an higher role - she composes from the demand from the producers of the anime or from her own inspiration, and if the anime or if she's in the mood of composing something clear and high, she won't volontarily darken the song with Keiko being the lead singer. When Keiko will say "I'm not happy with what I'm doing with Kalafina", she can do like Maya did, I don't think she's enslaved, plus she's gotten enough recognition with Kalafina to be able to make something else if she wants to.
On the other side, still agreeing for the commercial thing, but that's no use to complain again and again, that's a fact against which we can't do anything, that's the price of success. I can't help but console myself thinking that this is good for them to be more and more known, so that Kalafina can last and keep on giving us great non tie-in songs aside.
Sorry for this long disgression. Back to the topic, I'm getting more and more expectations from this single. Something like Hikari no Senritsu, which I personnally enjoy - I know I'm pretty the only one -, or Moonfesta, a song that is meant to give courage and energy, with traditionnal instruments, that can give something really great, if only there's finally no more "background beat" nor sudden disruptions in rhythm and singing like in the three previous releases.