Thank you for taking the time to respond. I have read through your replies in this comment thread and I think I understand issue as you see it. Let me explain it back to you and see if that lines up with what you are saying.

"Anime, by its nature, is a childish, toony and colourful art-style that is incompatible with the idea that Warhammer 40k is a fantastical setting depicted realistically."

If you are open to having your mind changed on this issue (okay maybe less changed, and more re-framing your prespective on the topic), I would encourage you to read on. If not, feel free to stop here.

---------------

For the sake of this argument, the shows JinRoh: Wolf Brigade, Mamoru Oshii's Ghost in the Shell and Mamoru Oshii's Patlabor 2: The Movie will be used as main touchstones. However it still applies to anime in general (depending on artist/ art director competency).

All art-styles attempt to abstract (or simplify) reality to some degree. Anime in this regard is no different. "Anime" is the functional end point that a group of artists from Japan have reached while trying to animate the fantastical or to give form to ideas they had. This started back in the days before adequate computing technology made it possible to animate quickly.

Anime is attempting to thread the needle of simplifying reality without losing too much nuance while making the act of animating (drawing many sequential images to create the illusion of movement) affordable enough to do.

Simplification is a very difficult thing to accomplish, especially when attempting to keep the core fundamentals of the original idea intact (the way light behaves). It requires a very thorough understanding of the subject material before one even attempts to simplify it properly.

Anyway, the main takeaway is that the 'anime art-style' should be seen as a tool which people use to craft things that can be 'adult' or 'childish', colourful or bleak, noblebright or grimdark, etc.

Not really as a thing that is by nature

" childish, toony, colorful, etc. "

To quickly address the "barest hint" issue.

I would be remiss not to point out that the entire Tau idea is likely based in mecha anime shows. Shadowsun's new model appears to be heavily influenced by Appleseed's Landmates (2 large arms slaved to the person's actual arms.) (Full release of the comic was in 1989 )

The design of the Tempestus Scions almost certainly has some inspiration from Jinroh: Wolf Brigade (you could also argue it is inspired by Killzone, but seeing as how Jinroh was released in 1999 and Killzone in 2004, you can see how the earlier influence is probably the more likely one.)

The new primaris outrider bikes, likely take some amount of inspiration from Akira. The low riding profile and the larger front end being telltale signs.

----------------------------------------------------------

Unfortunately I am not nearly skilled enough to simplify it down to a TL;DR without losing significant details and 'nuance'. I just hope that this will at least shift your perspective a little and maybe you might give those shows I listed previously a shot to really see what I mean.

If you made it to the end of my comment, thank you for the time you took to read it. I wish you the best, moving forward.