I think if Sakurai continues to pick 3rd parties via DLC these are the characters to look out for. For FP5 its possible that no company will repeat so that should eliminate Sega, Square-Enix, Microsoft, and SNK. After FP5 all bets are off.
Bethesda
Doom Slayer (Doom)
Dragonborn (Skyrim)
SNK
Kyo Kusanagi (King of Fighters)
Nakoruru or Haohmaru (Samurai Showdown)
Marco (Metal Slug)
Activision
Crash Bandicoot (Crash Bandicoot)
Tracer (Overwatch)
Spyro (Spyro)
Koei Tecmo
Ryu Hayabusa (Ninja Gaiden)
Kasumi (Dead or Alive)
Level 5
Jibanyan (Yo-Kai Watch)
Professor Layton (Professor Layton)
Ubisoft
Ezio Auditore (Assassin's Creed)
Rayman (Rayman)
Capcom
Jill Valentine or Leon Kennedy (Resident Evil)
Monster Hunter (Monster Hunter)
Dante (Devil May Cry)
Phoenix Wright (Ace Attorney)
Namco
Heihachi, Jin, or Kazuya Mishima (Tekken)
Lloyd Irving (Tales of Symphonia)
Siegfried/Nightmare (Soul Edge/Calibur)
Solaire or Chosen Undead (Dark Souls)
KOS-MOS (Xenosaga)
Konami
Frogger (Frogger)
Microsoft
Master Chief (Halo)
Steve (Minecraft)
Square-Enix
Geno (Super Mario RPG)
Lara Croft (Tomb Raider)
Sora (Kingdom Hearts)
Arc System Works
Sol Badguy (Guilty Gear)
Ragna the Bloodedge (BlazBlue)
Sega
Arle Nadja (Puyo-Puyo)
Sony
Nathan Drake (Uncharted)
Kratos (God of War)