Not sure about anyone else BUT
When I am too lazy to mouse I hit (Down Arrow) then (Enter) and my single choice box gets selected via KB
Surprisingly, that works. I say it's surprising because I've tried it in other games and had to do ridiculous things like up, down, up, before it selects anything. Those games must just have bugs. It's interesting what does and does not work, though. Auto mode has only worked on some games. That's fine as I don't want to use auto mode. In one game on which it worked it sped through so fast I couldn't catch all the dialogue (yes, I tried adjusting the auto speed in the settings, no effect,) and besides I like to control the speed manually so I can pause where I feel it has an impact on my experience.
Using the keyboard doesn't resolve my issue with the buttons anyway, which is that they appear in the middle of a sex scene and break me out of the scene (as I've said, I'm fine with them as dramatic pauses when doing things like knocking or opening doors to 3 adorable super cute girls who I'm meeting for the first time.) Even if I could hit the button lightning fast it is a visual distraction that takes my brain from "sex with hot girl" to "look, button!"
But Dammed is planning a solution which should make everyone happy and we all win!