If the replacement for the A-10 is a rebuilt A-10, then the new version will need new engines as well as avionics. The TF-34 is a 50+ year old design that is getting hard to support. There are a lot of modern engines in the TF-34/10,000 lb thrust class, including the latest version of the CF-34 which was derived from the TF-34. But methinks that the requirements folks will come up with requirements that the A-10 simply cannot meet. And maybe there's a new weapon in the works (a directed energy weapon maybe?) around which the new aircraft can be designed, much as the A-10 was designed around the GAU-8.
On a side note, with the current re-wing program already in place, the A-10 fleet will be flyable till 2028. That's "only" 12 years away. In today's environment, 12 years will be barely enough to develop, test, and field a replacement aircraft. Doing requirements definition today may already be too late.