a) User Interface is not a word that should be used here. Maybe Control scheme or something with control, but not UI
b) We already have differences in control - touchpad, gamepad, joystick, mouse, keyboard, touchscreen. Every device need different settings so adding possibility to control rotation won’t be making anything more different than it already is
c) Well, game over for you. There are many games in which you have full control over your character. And I’m not speaking about VR FPP game level control.
d) CI4,5 and Universe is perfect example of not 100% control, because you have here rotating mechanic which has effect on your spaceship and you don’t have any way to prevent or activate it so you don’t have control over it - not-100% control.
e) Whether you like it or not, Chicken Invaders is a SHMUP game and starting from CI4 it is no more only vertical scrolling shmup. Defining mechanic of Chicken Invaders is that you shoot chickens with spaceship that you control.
f) Not having control over rotations of your spaceship is not making the game challenging, it makes it longer (You must wait for a game to kindly rotate you in wanted direction) and less dynamic (which means it’s also more boring).
g) I’m not saying that we need to immediately make CIU have control over rotation. I just want it to become a thing in the future (hopefully soon future). Good game to look up
h) I’m not also saying that we should take a big leap and make CIU twin-stick shooter (to be honest I don’t played any twin-stick space shooters so I can’t provide example) or VR 3D area shooter (The Lab - Xortex 26XX).