^Ah, thank you very much! I shall continue with my double-posting ways then.
[Warning: wild speculation ahead]
Yeah, KOTOKO leaving is just... out of nowhere. I think it might have been a really sudden decision, because between Epsilon no Fune and this day, she released three singles (not to mention many eroge songs) while still under I've - that's often been the amount indicating a future album release for KOTOKO and Mami. That, coupled with the large amount of I've-produced songs on Hiraku Uchuu Pocket, seems to imply (to me, at least) she was already working on an album with I've and for one reason or another switched labels and got new friends on the producing list halfway through. It's not like she's hanging on to I've at all now that the departure's been announced (which would make the whole leaving-the-group thing questionable); instead, she's pumping out non-I've songs left and right. She already has like... three non-I've eroge songs coming up. Not to mention a new single, the opening for Shakugan no Shana III, has also been announced. But it doesn't seem like a simple matter at all and my speculation has yet to reach a conclusion.
Speaking of KOTOKO's new non-I've songs, here's one example: Pray's Color -Link- for a game called Mashiro Summer.
At least the split from I've has her take some new musical paths. This definitely doesn't sound like every I've song she ever did, which I was slightly afraid might have happened. But it's still clearly KOTOKO, which is always good.
And to elaborate about the Shakugan no Shana theme song: it's called Light My Fire, has lyrics, composition and arrangement by ryo (supercell) and will be released as a single on November 16th. KOTOKO sure seems to have a hectic release schedule after the label switch. o_o A single only a month after an album release? Wow.