It would be a nice change, but they intentionally switched Brock with Tracey, and again Tracey with Brock.
I've heard that they changed Brock with Tracey when they started getting scared of the possibilities of people relating Brock to racist theories and creating a conflict just like with Jynx.
Later, when they found out that nobody actually thought that way anymore (or never did), they found it totally safe to bring Brock back.
But the reinforced reason to bring Brock back even after knowing that he isn't a problem anymore was that Tracey had minor part to play in each episode, and didn't do much except sketching.
Tracey was mostly quiet the other times, and so was switched with Brock again with a good reason given, since Brock plays a nice part in each episode, adds a comic relief in almost all episodes, acts as a parent figure unknowingly, cooks food for extra fun, has nice basic knowledge to share about Pokemon with the viewers of the show which Tracey didn't, and all in all is a pretty visible character.