If we're being totally honest about echos. I see a lot of people clamoring over the ideas for echos.
Here are my opinions regarding them.
1. Most of the echos will probably not be revealed. They will most likely be kept a secret till the game comes out to surprise people.
2. A lot of ppl are asking for too many changes from echos such as a new move or whatever. When thinking of an echo lets look at Dark Pit and Lucina. Lucina has the changes in tipper and is 1 pixel shorter or whatever. Nothing else. Dark Pit has only 3 moves that are different (aside from a smaller rapid jab finisher hitbox) so barely anything. So if they are an echo fighter not much will be altered.
3. Some chars simply dont work due to the way the fighter is. Dixie can work but they have to make it so she lacks a rapid jab which is the one move diddy uses his tail in. But even then she isnt all that likely just due to her body and hair.
Anyways I guess Ill talk about who I think has a chance in terms of echo fighter choices. I doubt we will get more than maybe 3 or 4. Anyways...
1. Dark Samus. This seems like the easiest and the lack of a Dark Samus alt might be a hint. We already have a model for her from the wii u and shes popular. She would be the easiest and safest bet to add. We also probs wouldnt get mad at a "dark" alt because we already had Dark Pit to warm us up. Idk what her changes would be but she seems like the most likely choice. Especially with the high demand for more Metroid characters, more villains, more girls, and with Metroid Returns having happened recently and Metroid Prime 4 coming from. Dark Samus is the most likely character to get in as a Echo Fighter.
After this I would't say theyre ordered btw.
2. Octoling. Splatoon is incredibly popular and Octolings share basically the same exact model as inkling aside from a different head. They also again serve as more female and villain representatives. People have been wanting villains for a while and Octolings fit that bill. Very little has to be changed for them to work and it adds another splatoon rep when honestly there really arent many options for another splatoon rep (the sisters are a assist). So theyre a good and safe pick.
3. Medusa. Another female villain. Medusa is also an iconic NES era villain and works as a dark foil to Palutena. Again, basically nothing has to be changed since Palu and Medusa share the same build and staff. Theyre also sisters to them using the same moves doesnt seem weird in any way. Also consider KIU being so popular and it would add another character that would be easy to implement but stand out visually. She has also been seen in several leaks or at least said to be in several leaks so it feels like a safe bet.
4. Ken. Aside from being the ONLY other SF character to get a trophy in smash 4, Ken was BORN as basically an echo fighter of Ryu. Legit just make his SRK a multihit with fire, and his side b be a multihit and bam youre done. Hes a super popular character and is legit the same exact build as Ryu and is only a head swap. He would be super easy to add and considering he was basically an echo of Ryu for years and birthed the whole "clone" thing it makes sense. Also a ton of people love Ken and capcom seems to be buddy buddy with nintendo at this point so its not really asking for too much here.
5. Shadow. Im not exactly fully on board for this one but considering his AT is MIA and sonics very very close relationship with Nintendo now it wouldnt be a stretch. He also wouldnt require any animation changes. Also hes literally just a dark clone of sonic so it makes sense. Im not 100% sure on this one but he seems likely. Hes extremely popular, and heavily requested similar to Daisy. But he isnt really different enough from Sonic to fully justify a new moveset. They also explicitly showed of knuckles. So I can understand and see Shadow having a shot.
6. Raiden/Big Boss/Venom Snake. One of these 3 are possible. I dont think itll happen but Big Boss is EXTREMELY popular and Snake lacks any Big Boss skins. Raiden and Venom also work. Either of these 3 are possibilities but Im not sure about them. Just throwing that its possible.
7. Chrom. Another not too likely choice, but considering hes MIA in everything we've seen from Robin there is the possibility. Especially with his popularity and being so highly requested by people. Chrom might actually get off the floor now. Again I dont see it being all that likely but the possibility is there.
8. Zack Fair. While I HIGHLY doubt this will happen. He is Clouds mentor and they share the same body type (head is different) and same weapon and all around moves so its possible but I doubt it will happen. *shrug*
9. Ms. PacMan. While I think she works better as a skin and shes not really requested. You really cant throw out the possibility I guess.
10. Funky Kong. While not hugely requested, he is relatively popular and would add another DK rep which the series poorly needs. He also shares the exact same build as DK and would be insanely super easy to add. Especially since the model for him already exists and hes relevant enough to be playable in the newest DKC game.
11. Dixie. While possible Im not counting on it due to her lack of tail and hair. But you never know. People want her so maybe. I just dont think its likely due to her body.
I think overall the MOST likely are Dark Samus, Octoling, Medusa, Ken, Big Boss/Raiden/Venom, Chrom, and/or Shadow. Mostly because all these characters by essence are already basically clones of the original in some way or a dark version of an existing character (aside from Chrom)
But these are my thoughts on the possible echo fighters.
Again people NEED to remember an echo fighter only changes barely anything and shares the same basic body type. Very little is changed from the original. We know this just because chars like Pichu, Y.Link, Doc, etc ARENT considered echos.