I personally don't think it should. Xehanort is a key part of the series and has been the main enemy since day 1. It would be like the Harry Potter series continuing after Deathly Hallows. It is not necessary to continue the series after Sora and Xehanort's epic final confrontation (which will no doubt take place in KH3). Starting something else will make it feel totally forced and pointless unless they plan a having a series with an older Sora as master training a young apprentice. But even then, what would be the point?