The customization was terrible in my opinion. Every single CAF looked similar. You couldn't customize the banner behind you, customizing the fight shorts was very restrictive.
Another thing was how only certain fighters do certain things. I am pretty sure more fighters than just Chuck Liddell can throw an overhand right. Things like that kinda sucked.
It is good to hear that they are adding new disciplines and the southpaw stance. I am confused as to why they would leave out a southpaw stance to begin with.
The career mode is an easy fix. All they need to do is let your guy actually age, don't put a limit on how long you can fight, and allow the player to move weight classes. Then the older your fighter gets, the harder it is to maintain their skills. They start slowing down. That is exactly why Fight Nights career mode has always been great.