It would be more convenient. Given that this is supposedly a security feature - no. Nope. Not at all: what is the state of the data line(s), and how do you know that it matches whatever indicator the cable uses? (There's no way to tell, and you don't - if software is involved, securing stuff becomes HARD, and proving security even harder.)

OTOH, a USB Y-cable physically has no data lines connected on the extra USB-A male connector; it thus provides a far stronger guarantee that there is no data travelling across them. (Not foolproof, but safer than a software-controlled switch.)