According to Ishitobi, Subaru is “discussing [the program] internally,” but it’s almost a given that such models will be produced. In Japan, models such as the Legacy already have limited edition STI tuned cars available.
STI upgrades for the WRX have included improved differentials, a turbocharger, lighter alloy wheels, and Brembo brakes, as well as changes to the aero kit, and we would expect similar upgrades for any future models.