Upgrading "The Ten" is a relatively low-cost endeavor for Cessna; its basically the Sovereign fuselage (which was a little longer than X) with new engines (probably derated versions of the new 3007A2 for the Legacy 650) and Winglet Partners sails, a redesigned interior and a new avionics package...and an allegedly higher MMo. No additional fuel or baggage capacity, no bigger fuselage cross-section, no redesigned wing, nada. It also will provide them a "test bed" for putting G5000 in Sovereign (ending the Honeywell EPIC nightmare for Cessna) and possibly down into smaller models.
That's a LOT less R&D expense than would be necessary for a clean-sheet replacement for Excel, or even putting a Sovereign wing on that fuselage.
Besides, I don't think anybody really thinks they outright killed Fatation (aka Columbus) as their top-of-the-line aircraft...its probably waiting for next year's NBAA, hopefully after the industry furthers its turnaround, and hopefully tweaked even more to compete better in that crowded segment.