I have an advice... while you can't put a World 9 into the game you can still make it seem like there is a World 9 in the game by making one specific level of each world have a night theme (Or day theme/less dangerous appearance for Frosted Glacier and World 8) which will give that special/Rainbow Road feeling.

Yeah after searching the entire level a lot of times I knew it that the only place left would be in the lava but I wasn't so sure because I've played other hacks where there are missing Star Coins so I thought you forgot about it too, but now I have already 100% Cleared the game so it is fine and yeah it would be great if you do some update on it, the game was great but World 7 looked really blank since it didn't really have any major graphical changes from the original.

For me personally I'm okay with all the worlds, the only one that didn't catch my attention was World 7.