How long ago did you see Cruise cars doing these things?

Both Cruise and Waymo have remote operators who can direct the cars when they phone home.

Here's an example Vogt discusses a bit: https://youtu.be/sliYTyRpRB8?t=202

...of course this brings up many other problems, like network connectivity and inter-city transport, which the companies have as far as I know not commented on. IMO the sensible solution is obviously to just require passengers be able to take over if given plenty of warning, but for whatever reason Cruise isn't doing this.

3mm is about a third of total tread depth, and 1% of the tire's radius. Why wouldn't this be detectable? ABS sensors tend to have 48-tooth tone rings and there's no reason why you couldn't vastly increase this number if you wanted.

Longitudinal tire slip is caused by thrust in excess of the tire's grip, which is a function of slip speed among many other things. Grip peaks with a mild amount of slip, but slip isn't the norm outside of racing. Mild acceleration produces zero slip.

Lateral slip angle is a different story.

The slip is only 0 when free rolling by definition of the rolling radius.

You also have the rolling radius depend on load (car mass) and tire pressure.

I don't say I know it is impossible, but it feels like there is way to much noise.

It does if you have a GPS speed input. In the race car daq I use I can see speed differentials due to tire wear.

A typical 17" tire has a radius of 318 mm and 8 mm of tread. So a bald tire is 2.5% smaller than a new one.