Everyone has their own preference for how they like their game to be/look like. It should also be noted that there might be a minority of people that cannot play due to some issues they may face in-game. I'm not just taking about server issues, bugs, etc. I mean like things like Motion-Sickness, Flashing lights, UI readability etc. Here are some features/settings that should considered to be added the game.
Accessibility Tab: Self-explanatory. This tab in Settings will allow the user to toggle certain aspects of the game to help them experience the game better. Whether it is for customization purposes, or for actual health purposes.
Motion Sickness Control: Settings that can help reduce motion sickness. It is not uncommon for players to become nauseous when playing the game. As having Motion Blur or High FOV for too long, usually if their FOV is more than 90, can result of the player becoming sick. Having more options that can help people control their motion sickness better in-game would be nice.
Colorblind Settings: This first talked about when Mad-Eye mentioned it in a stream a few years ago. This feature should be added to help players who suffer from colorblindness so that they can better differentiate the keys that they need. This could also be used to them with customization options aswell.
Epilepsy Settings: Although the game, finally, has a warning about players who suffer from epileptic seizures, it would be better if there could be some options that could help reduce the chances of one occurring. Add options to reduce the effect of flashing lights and the intensity of them up to a certain amount. For example, one of the most common light flashes would be Leader's Teamwork skill, and being abled to slightly decrease the intensity of it would be very nice.
UI Settings: This feature would allow the user to increase the size of the UI text, remove annoying UI icons like the Status Effects and help them read the UI better if they need to.