As much as I'd like to say so, I doubt it. Young Link was replaced by Toon Link, and it would appear that it's going to stay like that due to Toon Link's visual individuality. He adds more variety to the cast with his cel-shaded appearance. Roy, despite being completely different from Ike, was replaced with him in a way. They share "similar," and I use that term loosely, Neutral B's. Ike would also be considered more fit to return, time restraints aside, due to his uniqueness from Marth. Both have basically been replaced, leaving Dr. Mario as the only one unreplaced, though I consider his absence unmissed, as he is a direct clone of Mario.
Now, also consider that Roy would require a completely a completely new model and fairly largely modified hitboxes due to his differences from Marth. The same goes for Young Link. Dr. Mario simply requires redressing Mario as a Doctor. He needs minimal model edits and no hitbox changes. In addition, Dr. Mario is also very different from Mario in his Down B: Dr. Tornado. This wouldn't even have to be created totally new, as some data can be ported from Luigi's Luigi Cyclone. Heck, you can even reuse voice clips, a property no other clone can claim. After all that's done, its a matter of replacing textures and other minor properties, and you've basically got Dr. Mario. Much easier that Young Link or Roy. Finally, I think Sakurai kind of knew no one liked FLUDD, so he may have selected Dr. Mario because he can be Pre-Brawl Mario.
I actually prefer Doc because of Dr. Tornado and several other small things, plus the fact that Dr. Mario is cooler than Mario by a runway.
You may have noticed that I left out Pichu. This is because I think he's a special case. Pichu, well, no one really liked Pichu, period. End of story. Yes, he has a very vocal fanbase (which I am proud to be part of), but I admit we are a minority. Pichu would have required smaller model edits than Roy and Young Link, similar to Marth is to Lucina, another "model swap." His hitbox changes would have very large, similar to what Roy would have required, but not to the extent of Link and Young Link. All that's left after that is porting Pikachu's moveset and recording new voice clips. His changes are arguably more drastic than the ones Dr. Mario required. And then, no one liked him. He was a joke character. That is probably the most massive reason as to why he failed to return. Had he been done differently in Melee, he might be in Smash 4, either alongside Doc or replacing him. I don't know. Honestly, I like Pichu a lot, but I'd much rather have Doc. He's Pre-Brawl Mario, and I used to play Mario until he got FLUDD, and the community, as a whole, would much rather have Dr. Mario.