Some cars do this. Audi and Porsche (if I recall correctly) use the disc brakes for the first couple stops each drive to knock off the rust if there's any build up. I think I remember reading that Ford uses the real brakes if you're under 5mph. I'm sure other manufacturers do something similar (other than Tesla which apparently doesn't do anything to help).

I don't think that is a good feel, you sort of get a feel for how fast you slow down with regenerative braking and throwing real brakes into the mix randomly sometimes would make for a horrible driving experience.

Better to have a reminder, surely the car could figure that one out.

Do we know rust on brakes is even a problem before assuming the electronics aren't smart enough?

If anything unsafe happens when you slam on your brakes, you need to get your car serviced. Just do it on a quiet street and check your rearview mirror for someone following too closely (a good habit any time you brake).