I think you are asking for something that is not available on the market.

It turns out there are products, but they are commercial rather than residential. Which doesn't mean you can't order or use them, but expect more setup required.

After more digging, it seems that "warm dim" or variations thereof is a marketing term that manufacturers have coalesced around to describe lights that start at ~3000k and dim to the 2000s or below.

For the commercial sector, the term "Tunable White" or TW refers to lights that generally go between 6000k and 2000k and have the ability to control dimming (i.e. lumen output) and color temperature independently - or in a correlated, mapped fashion.

https://alphabetlighting.com/products/downlights/nu/nu4rd-xicato.html

https://www.intenselighting.com/en/products/mxdrtltw

https://www.focalpointlights.com/products/downlight/id-35-downlight-trimless-flc3d-rt

The Alphabet Lighting NU line is probably the best for residential use, as it can be ordered with a bluetooth radio for remote configuration. For my use case, that means setting the maximum color temp to 4000k and enabling a logarithmic dim to 1800k. That setting is saved as the dimming profile on the light, and then a "dumb" 0-10V dimmer, Lutron or whatever is sold at the big box store, is run to the light and whoever is controlling the light from the dimmer is operating within the color temperature mapping you configured via the app. This gets around the need for dual-dimmers, one for color temp, one for lumens.

The Alphabet lights were the only ones that offered the mix of features we needed for a bathroom (IC, wet rated, high lumens, trimless) but I'm linking to the other manufacturers just in case someone has this same question in the future.

Hopefully as the market matures, it's easier for consumers looking for residential lighting products to get to the solution I ended up finding. I don't have a quote yet, but these lights are not cheap - expect $100s up to $500 per.

As this comment recently was liked, I wanted to follow-up again with the ultimate product I went with.

Element Lighting's 4" tunable white downlights. With no app/smart functionality, it was exactly what I wanted. They start at 4000K, dim to 1800K, 90+ CRI, can be flangeless, round or square, and support shower (wet) trims even in flangeless design - and are IC rated. http://www.element-lighting.com/Products/Details/4-LED-Fixed-Downlight

I ordered the high output, flangless, shower trim 4" round version, "E4RL-LHTW416ODI-ELT0". The ELT0 designation at the end is critical, as that designates the built-in driver to use 0-10V signals for dimming/color change, which makes the lights compatible with "dumb" ELV dimmers like Lutron's DVSTV. You can wire both the dimming (luminosity) and color change channels to one single ELV dimmer to get warm-to-dim functionality, or use two dimmers to independently control color temp and lumen output.

One thing I wish I had done differently is to get the logarithmic dimmer instead of linear. I have lumens/color ganged to a single dimmer, and if the lights aren't at 100% output (4000K), I find I'm fiddling with them at ~5-10% output to get that nice warm glow. A log dimmer response would give you more control in the low/warm (1800K) region.

I bought WAC spots with the warm to dim bulbs, but found the warm was too orangey. I ended up getting new spots and Hue bulbs.

Not that I understand it, but my understanding is that if the LED controller is logarithmic, then you want a linear dimmer. and vice-versa. IOW, the dimmer technology needs to be oppositely-paired to the specific LED, at least in terms of tunable white.

This is another differentiator of warm-to-dim functionality. Warm to dim LED's are designed with the dimming algorithm baked in. So, unlike tunable white, warm dim aren't as sensitive to the dimmer's algorithm (they just dim like any other pure color LED).