I'm sorry, if you think that Nomura wasn't always going to find a way to revive Roxas, Namine, or Xion for that matter, then I don't know what to tell you. The revival plot was around at least since kh2 Final Mix.
KH3 was always going to be about Sora fighting off a complete version of Xehanort and saving people who were lost. I don't think it ever had potential to be anything other than that. The fact that TAV were in vanilla KH2 also leads me to believe he wanted them to be saved too. The unplanned plot-point of the saga seems to be DDD, considering it was conjured up way after the post-2 trilogy that was announced within months of kh2fm coming out. And that before DDD there was going to be another "Mystery Game" that got shelved.
The plot and cast are bloated, but not surprising. I don't think KH3 could have ever been anything other than some version of this revival plot.