Well, it says "volume 2" not season 2, and also "Ryuuko Matoi & Senketsu vs Satsuki Kiryuuin & Junketsu", so the odds of it being a season 2 poster are pretty abysmal :p
I'd also prefer a new TRIGGER anime altogether than a Kill la Kill sequel.
KlK's ending was kinda satisfying as it is(presuming the Ova coming out in September will be the epilogue which I felt was lacking in the anime itself), so let's leave it that way.
Did not Hououmaru fuse with Ragyu's omnisilk just after she dressed it? I think Rei's not an issue...
I don't think so either if we take in account that Nui also fused with Ragyo. It wouldn't make sense that a human made it out alive after Ragyo was totally stripped from her Kamui whereas a living Life Fiber like Nui actually would have a better chance of coming out than Rei. As much as you would if a Kamui actually got absorbed and dissipated anyway.