I think this could be very interesting, if done properly. I want this to be post canon, with everyone minus Light looking back on everything Kira accomplished and viewing the intricacies of his various plans. This also means that L will come back to life to watch the proceedings, and the same goes for any other deceased characters that were at one point relevant to the plot throughout the story. Maybe add Ryuk and Rem as well, with a sub-plot of Ryuk and Rem talking about Light in a more shinigami-esque manner. Perhaps even have some theorization/speculation around Light's fate after death, such as if Mu (nothingness) actually refers to the shinigami realm as that nothingness, or if Light became a shinigami or not.