We all know about EX red focus can create new combos. It provides a way for just about every character to combo into Ultra off a move with a lot of hit stun, like a heavy attack. Some character like Ryu can combo into their heavy attack, but the guys who'll have the easiest time are the guys who have a special that doesn't knockdown nor does it have a lot of push back. This is what I found off the top of my head
Evil Ryu: cr. MK, LK axe kick, EX red focus, Ultra 2 = 469 damage
Yun: cr. MK, LP shoulder, EX red focus, Ultra 1, HP lunge = 457 damage
Yang: cr. MK, LP slash, EX red focus, Ultra 1 = 394
Oni: MP, LK slash, EX red focus, Ultra 2 = 499 damage
Viper: cr. MK, MP knuckle, EX red focus, Ultra 2 = 455 damage
Makoto: cr. MP, LP dash punch, EX red focus, Ultra 1 = 426 damage
I'm probably missing a few others but these are basically the characters that fish for EX red focus very easily compared to the rest of the cast. Not everything up there is a true block string or safe on block, but regardless they are hard to punish for most people or can't be punished. These guys will have a far easier time taking advantage of this new mechanic compared to most of the cast. Luckily for me, I play two of those characters with Evil Ryu being my main. Unfortunately everybody else their including Viper