I think everything that is need to be done to the Vader Castle cameo is:
-Include the altered Rogue One shot from the Castle with the Ties and colour correction Ziggy has linked
-Add the awesome Movies Remastered edit of the Castle Behind Kylo when he holds the Wayfinder
That’s it. We got a proper Mustafar appearance with a satisfying Vader Castle cameo (the original one of the movie I barely recognize if I haven’t read it online) and a Coruscant nice easter egg in the movie.
A proper Vader Castle cameo is just so good because ties the sequel trilogy with Rogue One, making the Disney Era more interconnected. We all go to cinema in 2016 and watched Rogue One, wondering if elements from that movie would appear on the other movies of the sequels. To be better than this, only if we find a way to include something from Solo, but I have no idea really.