There is a video I found that is related to this discussion. This video is made by Mr. Pickle, a Smash Youtuber who uploads mostly Melee videos. Surprisingly, this youtuber uploads a video about Smash Switch (When I mean suprising, most Melee players were very finicky in each Smash game because they want it to be like Melee, so they are more disinterested in the next iteration in comparison to the Smash 4 players). In this video, Mr. Pickles gives his thoughts and predictions of his top 4 Smash 4 characters that may not return in Smash Switch.
Here is the video:
If you are unable to watch the video, I'll list the top 4 characters that may not make the cut and copied his key explanation and reasons why they couldn't make the cut.
4:

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Reason: No Longer Relevant, Replaced by Newer FE Character
Explanation:
"Characters are often added to Smash that are relevant to other games popular at that time, not only for fan-service but to also advertise those games. Smash 4 took full advantage of this by adding two new Fire Emblem reps,
Robin and
Corrin."
"Now, however, approximately 3 years later, the games associated with these characters are no longer the newest in the series, and thus there are newer characters that will likely replace them - similar to how
Ike replace
Roy in Brawl."
"With
Fire Emblem: Echoes being released in 2017, the main protagonist -
Alm and
Celica are most likely to replace Robin and Corrin if they're removed. Robin and Corrin may very well be here to stay, just like Marth and Ike."
3:
Reason: No Longer Relevant, Replaced by Newer Pokemon
Explanation:
"Similar to the
Fire Emblem Franchise, the
Pokemon Franchise tends to have a new rep to represent the newest generation of Pokemon in each new game. In Melee, it was
Pichu. In Brawl, it was
Lucario, and in Smash 4, it was
Greninja."
"They may very well decide to place Greninja with a Gen 7 favorite like
Decidueye or perhaps even
Golisopod."
2. 3rd Party Characters (

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Reason: Lack of Collaboration between Companies
Explanation:
"Introduce in Brawl, 3rd party characters have always been important to the hype of Smash. However for a 3rd party character to happen both Nintendo and the fellow company must co-operate."
"Like what happened with Snake, there's a significant chance that a few 3rd party characters won't make it into Smash 5."
"Due to Nintendo's close ties with Sega, Sonic and Bayonetta should make a return. We can't be sure about anyone else though."
1. The Clones: (

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Reason: Unnecessary, Clones, Irrelevant
Explanation:
"Finally, there are three distinct "Clones" in Smash 4 who were added late into development:
Dr. Mario,
Lucina, and
Dark Pit. These were characters that could've been implemented easiy because of how similar they are to their original counterparts."
So...
What is your feedback about his predictions? Do you agree or disagree? If you don't want to look at the post, you can ignore it.
That is all for now...