For now there is a convenient way to do this:

<style>
   @import url("...") supports(...);
</style>

I wonder if making the media attribute inconsistent is worth it

At https://html.spec.whatwg.org/multipage/semantics.html#standard-metadata-names:meta-color-scheme, the spec normatively states this:

There must not be more than one meta element with its name attribute value set to an ASCII case-insensitive match for color-scheme per document.

But then later has this non-normative note that says this:

Because these rules check successive elements until they find a match, an author can provide multiple such values to handle fallback for legacy user agents. Opposite to how CSS fallback works for properties, the multiple meta elements needs to be arranged with the legacy values after the newer values.

So, that note seems to conflict with the normative requirements — by implying that using multiple <meta name=color-scheme> elements is OK (or even sort of a best practice).

(There’s also a grammar error in the note.)

So, maybe that note about using using multiple elements was written without an understanding that the value could be a list of keywords rather than a single keyword?

Regardless, the note seems wrong.

also would be surprising that media is ignored here:

<link rel=stylesheet cssconditions="supports(at-rule(@scope))" media="print">