That would potentially get into some weird territory though, if multiple characters are played by different actors in the sequel while Harley Quinn is still played by Margot Robbie.
Recasting one character is fine but multiple could get into a murky area that would just seem kind of weird.
But if Rick Flag is not in the film at all as has been reported, that would gel with the word that James Gunn will primarily be using DC characters that were not in the first movie.