The F-35 is supposed to replace the A-10, AV-8B and Marine F/A-18, along with all the aircraft that partners use for CAS.
Whether this will happen depends to some degree on how CAS requirements change. I suspect there will be a move towards a lower-cost, more persistent platform staying out of "golden BB" range, using DIRCM and reduced IR signature to defeat MANPADS, and radar/IR/Brimstone-equivalent against heavier air defenses.