First of all, welcome to DCW!
In one of the recent MK chapters, Gosho introduced a character that has a prosthetic eye (Goudzou), just like Rum supposedly does. Now I'm not going to suggest that he is Rum for obvious reasons. In the anime, we got to see how the prosthetic was portrayed, though through most of this episode, half of his glasses were shaded just like the manga. I'm not sure how this will translate to DC's anime, and if Kuroda will be showed in a similar light. After all, Magic Kaito 1412 was animated by A-1 Pictures.
As far as Magic Kaito and Detective Conan being related... well, there are definitely similarities for sure, but Gosho loves to reuse story elements (and character models, *cough cough*)
Here is basically what Gosho had to say dismissing that MK and DC are connected.
Not to sound like a broken record, but as far as the Rum has already appeared hint... I still think it's a good possibility that this could be referring to Lum's cameo since that hint coincided with that file, and that Gosho drew Lum as Rum back in 2007 for a panel honoring Urusei Yatsura. I just wouldn't be too quick to rule out any characters that showed up after that hint was made. He also added a laugh at the end of said hint, but... Gosho laughs at everything, it doesn't really mean anything. It's still a possibility that Rum could be an entirely new character that has not yet been introduced (and it's also entirely possible that he is one of many characters that have already been introduced).