I was thinking the same before but now I know it doesn't make sense.
Difference between DS and 3DS is huge comparing to one between GB and GBC.
DS and 3DS have similar designs but they are completely "two different worlds" in case of programming. Grey and R/S remakes must be decided to be made only for one console - DS or 3DS because they are very different systems.
Adding "3DS enhanced" elements into DS game would require reprogramming the whole game into 3DS system. And that doesn't seem likely they would put that much effort just to add some "3DS enhanced" details.