a quick Google search with keywords like 1536kHz DAC, there are about 367,000 results with links to actual products supporting 32-bit 1536kHz input.

Google fools itself. Go to the bottom of the page and click at page number six.
https://www.google.com/search?q=(%221536+kHz%22+OR+%221536kHz%22)+AND+%22DAC%22&start=50
Drop the "&start=50" and I also get 367 k. But scrolling to the end, it is only 56. Click for the search to include the alike-hits, and I get 236 of them in total.

Replace both 1536 by 768 and the 56 grow to 88 and the 236 to 389.

That is a reason to use WavPack. It handles 4 GiHz (like WAVE does).

Here's one such release on 768kHz.

Quote from: ktf on 2022-06-14 06:34:05

Here's one such release on 768kHz.

Wow... what a waste of space, recources, time, money. It contains almost HF-Noise.

almost HF-Noise

The best part is some of their 24-bit files are actually 16-bit.

Quote from: MrRom92 on 2022-06-14 01:30:24

In search of some older 32 bit files, I did come across some WAVs that were previously (and probably still are) incompressible, however due to another reason entirely - they are 24/768kHz, and the max sampling rate the FLAC encoder allows is 655.35kHz

This limit has been raised to 1,048,575Hz in April, which is the true limit of the format. The previous 655,350Hz was the 'streamable' limit of the format, for some reason the reference encoder (libFLAC) didn't accept anything with a higher samplerate than that.

Quote

Not that I expect any commercial music releases to ever use such a high sampling rate, nor do I think it would have any practical application to most people, but it does seem that 768kHz is somewhat of a standard sampling rate for audio analysis and some other professional applications. It would be nice to have them compressible as well, as it would seem to be a much more appropriate format for this purpose.

Here's one such release on 768kHz.

Quote

I do know that the Domesday Duplicator / ld-decode folks are using FLAC compression in some nonstandard manner for recordings of RF captures sampled at 33.5MHz (yes, with an M) so theoretically this should be possible with the standard encoder too, if not for the limitation being baked in.

Yes, I've recommended them to place the sample rate in a vorbis comment or something similar. The samplerate is nothing to the FLAC format but a number, it doesn't do anything with it except including it in the frame headers and giving it back on decoding. It really is only necessary to be able to properly play back a file.

I’ll have to give these 24/768 files a shot on the newer compile now too.

969 129 022 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.wav
967 864 784 TransposedTo192k.nometadata.wav
778 734 183 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.7z
703 857 334 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.fj0.wv
673 615 462 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.fast.ape
666 519 575 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.tta
663 164 138 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.hx1.wv
653 129 918 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.normal.ape
652 911 634 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.high.ape
650 586 694 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.m4a
649 644 648 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.-5.flac
649 459 286 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.extrahigh.ape
645 055 381 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.als-at-default-in-.mp4
643 043 026 TransposedTo192k.nometadata.-8p.flac
642 946 998 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.-8p.flac
641 225 096 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.wv-hhx6.=37min=.wv
640 902 644 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.wv480-hhx6.=40min=.wv
637 544 165 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.-z3.als
634 689 178 TransposedTo192k.nometadata.-p4m.tak
634 179 909 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.-7-t2.ALS-in.mp4
632 366 679 Let The Good Times Roll - Carmen Gomes Inc - Free 768kHz.ofr.max.ofr

FLAC git-c94b4f8f 20220626
Built on June 26, 2022, GCC 12.1.0
(Code Base : 1.3.4)

https://github.com/xiph/flac/commits/master

You need to apply the --lax option. By command-line, you throw in " --lax " before or after all the other options.

The only practical application I know of for such high sampling rates in terms of music production is capturing the bias signal present on tape to digitally correct temporal distortions, ie. Plangent Process

Also, maybe for situations when it's not really about sound, just some physical processes, maybe radio frequency even. (archives/test cases for software-defined radio?) Possibly useful if the signal may share some statistical properties with that of sound, making it somewhat compressible by similar algorithms.
(But then, even ~1Mhz might not be a high enough upper limit)

FLAC git-3022dad8 20220806
Built on August 06, 2022, GCC 12.1.0

As far as I am aware there is no PCM DAC that can truly operate at such frequency anyhow. Anything advertising sampling rates higher than 192kHZ is with all certainty using a delta-sigma chip. The non-oversampling converters capable of natively operating at 192kHz are already very few and far between.