What is the point of setting an upper limit in Auto-ISO?

I can't think of any reason why we couldn't be shown that all of the time that the EVF or LCD is active. There are always settings in place before we half-press.

... assuming that you did not normalize brightness. If you normalized it, the 6400 should be less noisy-looking with many cameras, and I think that normalization is a "given" in this context.

Many museums use very-warm broad-spectrum lights that create a lot of near-infrared which can put a magenta/purple cast on the objects based on their NIR reflectance. It's not an easy thing to fix. People who have cameras that are more sensitive to NIR need to be aware of the problem with "very warm" broad-spectrum lighting. This may be addressable with filters, but filters will lose some visible light, too, and the light may already be too low in such places.

I have found that the highlights in many dynamic scenes don't change much. In the two examples you posted, it doesn't look like they will.

I think the only advantage of A mode is saving time in post.

Lr definitely does a better job of pushing than pure multiplication.

Your arguments are based on the assumption that the minimum shutter speed is set to the absolute minimum that is tolerable, right on the edge of risking motion blur.

I'd rather increase that minimum shutter speed and set the max ISO a bit lower, hence having a better chance of avoiding motion blur at lower ISO, yet not push the camera to max ISO by doing so.

On my Nikon Z9 you can only change ISO value, not the minimum shutter speed. On Z 7II and Z6 II you cannot get to the ISO sensitivity feature at all via Fn button

In M mode, the shutter speed does not change and can lead to overexposure once the base ISO is reached.
In A mode, the camera's metering will increase the shutter speed when necessary to prevent overexposure.

I use a completely different exposure philosophy if it is possible to use base ISO.

On the other hand if your minimum shutter speed is high, it might lead to unnecessary high ISO.

It is unfortunate that we cannot assign Auto ISO (or d9 settings) to function buttons with Nikons while other manufacturers allow it. I have added it to MyMenu,

Less DOF than what other option? Less than with a slower lens, AOTBE, but not less DOF than a FF camera and lens giving the same photon noise and image-level diffraction. It's always down to the pupil size, and distance from the subject, for these three parameters for a given subject in given light and a given exposure time.

There's no reason that a camera couldn't have an option to increase the shutter speed beyond that set by the user in M mode, to avoid clipping highlights. That could be useful with both manual ISO and auto-ISO. Canon has already provided an option in some recent cameras that can change shutter speed in M mode when you zoom a zoom or add/remove TCs, so Canon could not claim that the option that I wish for would "go against the spirit of Manual".

If the camera is on a tripod, presumably you have plenty of time. In that situation, what possible advantage does auto ISO offer?

You cannot change shutter speed in auto ISO in my menu on Z9, but you can on Z 7II and Z 6II

Do opinions change if after a certain ISO noise reduction is applied, say 6400?

Some camera manufacturers appear to be applying some form of noise reduction (that isn't user controllable) after a certain ISO. -based on what I saw on that photonstophotons link earlier.

My philosophy of a raw image workflow is to never do anything in camera that can't be done at least as well in postproduction.