1. Extend 'b' to 'b[N]' which allows optionally specifying the number of seconds to disable the buttons, with the default for 'b' remaining 1 second. A reasonable max seconds could be enforced if that would be appropriate. b0 would clear the keyboard input buffer as 'b' currently does, without any delay.

2. New switch 'F[N]' or similar which allows you to set Focus for which button activates when the spacebar or <enter> is pressed. 'F' or 'F0' would cause none of the buttons to have the focus, 'F1' and 'F2' would be 1st and 2nd buttons respectively. Any N greater than the number of visible buttons would be same as 'F0'. If is easier to have the N be required with 'F', that's fine.

These would allow making sure the user has more than 1 second to read an important prompt message before responding.
Also allows changing the default action away from the 1st button
Also allows requires something more than spacebar or <enter> to trigger a reply
Also allows ignoring the existing contents of the keyboard input buffer without a delay.

sendkeys shows that in the absence of the 'b' switch, $input currently behaves like clicking on YES when there's a spacebar or <enter> already in the keyboard buffer.

//sendkeys $({,0) $(},0) | echo -a noop $input(test1,y) | echo -a noop $input(test2,y)
//sendkeys ~             | echo -a noop $input(test1,y) | echo -a noop $input(test2,y)

'b5' would allow 5 seconds for reading the prompt before accepting keyboard or mouse input. 'F0' would move the focus away from any of the buttons, requiring a <tab> before the spacebar or <enter> would activate a button.