regarding Haruhi - oh heck. I can just see Gendou smiling evilly at the Brigade, claiming it's important and all that bull that Rei's piloting Evangelions, Haruhi, of course is positively for it (her junior SOS-dan member becomes part of an ancient conspiracy!) and Kyon's facepalming as if there's no tomorrow.
Besides, the interesting similarities between Yuki und Rei.
Hm. Another interesting possibilty regarding a Guardian for Rei would be Belldandy, of AMG; I mean, Rei *is* somehow related to them.