It still irks me that Project Thor never got off the ground. That really would have been the silver bullet for CrossCountry.
As it is, I'd be looking at Crewe-Chester electrification (via whichever route makes most sense) and enough Pendolinos to free up the entire WCML 221 fleet (diesel dragging the handful of 390s that go beyond Chester) and MML electrification with a new fleet of EMUs (probably IEPs) to free up the entire Meridian fleet.
I'd hand over the whole 22x fleet to XC to run decent-length trains through the core, possibly splitting to serve the extremities. To my mind, there are far bigger electrification wins to be had than XC. The Voyagers have another 20-odd years of life in them and few useful cascade opportunities, so I don't think it's worth getting too worked up over electrification of XC yet. I think it makes more sense to run 22x largely under the wires than to pension them off prematurely.
Once we've done CP5 and CP6 electrification, we'll have a much clearer view of what's left for XC wiring. Hopefully by that time we'll be a long way into replacing 3rd rail and seriously looking at wires to Penzance and Aberdeen (maybe even Inverness) and when the Voyagers come of age, we'd be able to replace them entirely with EMUs, and continue to provide the bulk of through journeys currently on offer.