I would like to see Marcus’s Dad as guest character.
That’s not a guest character.
But Daddy Adam Fenix would be a nice, niche addition.
But just like Hoffman/Prescott, their VOs are just a little on the old side, with Adam’s being I think the oldest VO across the entire Gears’ cast. (85)

I am an E-day vet. I’ve been here since '06. I don’t know who Adam Fenix is but marcus’s dad would be a cool add
Markus Kruber, Bardin Goreksson, Sienna Fuegonasus, Victor Saltzpyre, Kerillian
Isaac Clarke
Geralt of Rivia
Yennefer of Vengerberg, Triss Merigold
Jutta an Dimun
Commander Shepard
Legion
Subject Zero
I ■■■■■■■ love the Witcher, the Books, show and Wild Hunt especially, but No. Just no. I can semi-forgive Halo for being 1) Xbox and 2) Sci-Fi, same with Terminator being beloved, badass and sci-fi. But a medevial band of Witchers and mages does not fit Gears (at least the human side) and would look so out of place.
NO to any of these Guest characters, I say just let people mod the PC version of the game at the very most.
William Shatner will be a cool character to see next.
None of these
This isnt smash brothers
You re right, but it should be.
We need Mario and Luigi.
Na just Marios cloths on Marcus with an expression that says "It’s a me Marcus’
I want duke nukem or gordon freeman of Half Life 
Or simply arnold Schwarzenegger Terminator … Dark fate version with cool glasses 
Better character design would be nice to be honest. The new Cog Gear armor is kinda of garbage. I don’t want the old one back just better design would be cool
“They a-■■■■■■-up my toma-toes!”
TL:DR.
After we get the rest of the gears cast I wouldn’t mind getting the rest of Noble team considering we already have Kat and Emile. However give them a full set of perks this time.
Another idea, let’s get John Wick in here like they did in PayDay2, only I want TC to get Keanu for the voice. For Horde his class can be The Baba Yaga. When he does an execution instead of a knife he uses a pencil 
Most of all. Besides Anya, Dizzy and Hoffman, I want Griffin back in here. WTH happened to him after gears 3? I’m sure Ice Tea would love to do the voice acting if they asked him.
maybe the characters off of bulletstorm or even Duke-Nukem lol
Since they have added so many WWE superstars I would legit pay hard cash to have Randy “Macho Man” Savage.
Or Griffin himself.
Bulletstorm is still Epic’s IP.
He’s expressed interest.