Made this mock up in photoshop of what I think the final roster might be
3 newcomers
6 echoes
Reasoning :
Dixie - Is Diddys echo. She lacks a jab finisher and her up b is her hair twirl. Visually her popgun is bubblegum shots. EXTREMELY popular character and has been wanted for years, and was cut from brawl.
Black Knight - Ike echo. Slightly tweaked animations. Up B is a warp like zeldas. The most popular FE villain and canonically has the same fighting style as ike. Would work to add a villain to the FE reps and would be very easy. Also had a mii outfit, the general in the back of castle siege was changed, and ikes black knight skin was tweaked.
Isabelle - A super popular character. Animations are different from villagers but is very similar. Has been leaked several times (dont believe leaks but eh) and had a mii outfit. Also missing from the ATs
Medusa - Relatively popular villain and the only NES era villain missing as well as nintendos main girl villain, something smash still lacks. DA and bair lack a shield and her specials are palus other specials from s4 since customs are gone.
Shadow - Missing AT and super popular. Up B is a warp. Mostly animation differences.
Ken - the first echo fighter ever. Also the only char aside from ryu who had a trophy or music in Smash 4. Up B and side b are multi hit and up b has fire effects
Skull Kid - Insanely popular, several hints at him already, missing AT that was replaced completely, only other zelda char that is on the level of the main 3.
Isaac - can be the retro pick I guess. HUGE fan demand, still missing from the ATs and was a super popular ballot choice.
Banjo - The only char i can honestly think to top ridley or K rool with most people. While I dont care about him, I know hes insanely popular to a ludicrous degree. Rare and microsoft both said theyd want to see him in last game but have been strangely quiet this time around