Jayhawk fan here: MU was our main rival (in a hatred way), but it's kinda nice that they are gone. I think it was getting out of hand. KSU has always been a rival but its not nearly as intense and more friendly.
I don't think most KU fans would see ISU as a rival. I think you guys are going to be good for years to come with Hoiberg, but throughout the Big 12 we've seen teams rise and fall. In the early years it was ISU, then Texas and aTm were good, KSU bounced back, now Baylor, OSU, and you guys are pretty good. We've had very good, competitive games with all those teams. But I don't think that just having good games between us makes us a rival. For years on end we beat KSU in bball, they beat us in fball, but the rivalry was still there.