I just had a realization about when or if the Kakashi/Kabuto rematch happens. Kakashi will no longer have much of an advantage with the Sharingan against Kabuto since Kabuto as well as Oro have been training Sasuke for the past 2 1/2 years. Sasuke who has the 3 tomoe Sharingan. By now, Kabuto must have already figured out all the true strengths and weaknesses of the Sharingan and perhaps made some adjustments. So now, the advantage that Kakashi had over him pre-timeskip probably won't work post-time skip, even though Kabuto was already smart enough not to show him any techniques of his, as well as percieving that Kakashi got tired easily from extended use of the Sharingan, unlike the Uchihas. If the Kakashi/Kabuto match happens, Kabuto will definitely be the one to look out for. Not to even mention what would happen if he has a demon like many people are theorizing. Just my observations.