There's an unused map icon that looks like Kris hidden in HGSS' data, which means that Lyra was a late addition. Given her strong resemblances to both Mario and RBY Red, I wouldn't be surprised if Nintendo meddling was involved. :rolleyes2:
That being said, there is also a noticeable trend of GF wanting to introduce a new player character with every remake. Since RBY only had a single male protagonist, FRLG could do it without replacing anyone, but that isn't the case with later remakes, so GF picks the most "expendable" protagonist and gives them the boot. Kris was only in Crystal instead of all three Gen 2 games, so she was seen as less "important" than Gold, and out she went for the Mario cosplayer.
GF was more subtle with ORAS. Brendan isn't officially considered replaced, but the ORAS boy hardly resembles him and is really just another guy wearing his clothes. Brendan was always depicted as having black hair, brown eyes, and fair skin, while the ORAS boy has brown hair, blue eyes, and a bronze tan. No other non-replaced protagonist changed that drastically, not even May from the same games. I wouldn't be surprised if the ORAS boy was originally intended to be a new character and was turned into "Brendan" later on.
Given past trends, things don't bode well for Lucas in DP remakes. While Dawn was a main character on the show for 4 years and became a fan favorite character, Lucas only got a very minor movie cameo and otherwise only seemed to exist to give Ash a new outfit. Not even Generations bothered to include him like all the other non-sequel male protagonists. That Lucas also happens to be a blatant Red clone, as well as arguably a male version of Dawn, doesn't help his case either.
At the very least, Lucas will get the "Orlando" treatment and be redesigned to the point of being barely recognizable while still officially being the "same" character, but I wouldn't be surprised if he got outright replaced. I don't think Lucas was ever as popular as even Brendan, and nowadays, he's probably one of the most forgotten player characters. Even Kris still gets remembered for being the first female protagonist, and Green gets remembered for almost becoming the first female protagonist (and being left out of everything Red and Blue are included in). But, Lucas? His biggest claim to fame is being Ash's DP outfit. You don't get any more "expendable" than that.