No. Originally, KC-X was the -135 replacement, KC-Y was the -10 replacement, and KC-Z was the not-sure-what-we'll-need-but-better-start-planning-something-anyway concept.
Last I heard, Big Blue is planning on the -10 being around until 2030 (and I hate to think about what kind of shape the -10 fleet will be in by then...). However, reference the BUFF, Bone, -135, U-2, and others I'm sure I missed, to see Blue's track record on their aircraft lifespan projections.
We've got some of those in the -10 too. If I had my way they'd all get kicked in the junk (whatever version of junk they possess).