Instead of being a "problem-ridden prototype," K.A.R.R. would now adopt the "new and improved" model, and can finally gain an upper hand on the new K.I.T.T. Plus, he will still be a Mustang to give a faint trace of the "evil twin" concept. Also, he should retain the old scanner style as this will be his original A.I. being resurrected, hence the scanner sort of being part of his "soul," so to speak. Also, if he returns, since Charles Graiman will most likely not be the one to rebuild K.A.R.R., Blackriver will be the ones to develop the technology which will also explain why the new duel-scanner won't be used for him.
Excuse the poor Photoshop as I'm not much of a Photoshopper:

Maybe someone else could tweak it some more and add some silver trim to the bottom?