For fun I decided to go through this entire thread to see what things actually came true in either Smash 4 or Smash Ultimate so far. Here's what I got. Seperated by speculation periods and years.
POST BRAWL/PRE - SMASH 4
2008 (Pages 1-25)
Miis (Lario)
Daisy (King Mario, Paper Striker)
Rosalina (Rosalina Spalko)
Death [Kind of? A scythe appears as an item. Might not exactly mean Castlevanias Death though] (Lario)
2009 (Pages 25-42)
Rosalina and Daisy (Mr. Yellow)
King K. Rool, Bowser Jr., Rosalina, (Booman)
Megaman (Aiko Heiwa)
Ryu (Glowsquid)
Daisy and Little Mac (Aiko Heiwa)
Koopalings (Iggy)
Ridley (Smugleaf)
2010 (Pages 42-50)
Ridley (Super Mario Bros. Baby Luigi)
Mega Man (3K, Falcon Facepalm)
Bowser Jr. (Spinymaster347, cpm)
Handheld Smash (Falcon Facepalm)
Masked Dedede as Final Smash (3K)
Miis (Falcon Facepalm)
Dark Samus (Baby Luigi)
Chain Chomp Assist Trophy (Falcon Facepalm)
Pac-Man (drseaweed)
2011 (Pages 50-58)
Young Link and Snake coming back, Pac-Man, Dark Samus (GalacticPetey)
Pichu (GalacticPetey, Koopa Kid)
Smash on 3DS (Koopa Kid, Neptune)
Bowser Jr. (GalacticPetey, -21)
Miis (Lily)
DURING SMASH 4 SPECULATION
2012 (Page 58-65)
Chain Chomp assist trophy (Yoshigo99)
Mega Man (Epic Nitwit)
2013 (Pages 65-71)
Bayonetta (GalacticPetey)
Rosalina (true_princess_rosalina)
2014 (Pages 71-82)
Koopalings (Shygul, User4042)
Miis (ernesth100)
Miiverse Stage (ernesth100)
Bowser Jr. (User4042)
Duck Hunt (Shy Guy Forever)
Ridley (Crackin355)
2015 (Pages 82-85)
Returning every previous character (MeltdownKP1)
Ridley (GalaticPetey)
POST-SMASH 4
2016 (Pages 85-86)
Daisy (Alex95)
2017 (Page 86-88)
(Nothing came into fruition)
2018 (88-90 [Ongoing])
Snake returning (George Jones)
And here's all the correct character predictions made in this thread.
Bowser Jr. 6
Miis 4
Daisy 4
Rosalina 4
Ridley 4
Mega Man 3
Koopalings 2
Dark Samus 2
Pac-Man 2
Snake 2
Pichu 2
K. Rool 1
Ryu 1
Little Mac 1
Young Link 1
Bayonetta 1
Duck Hunt 1
Guess the moral of the story is in a thread called "Far-fetched suggestions" you have 17 characters that made it in over 1700+ posts. There's an average of 1 character getting in Smash for every 100 posts! So I guess don't give up! :V