Very true. The models of the NUC that SimplyNUC and the fanless chassis vendors support are typically the Mainstream models that sell in higher volumes.
While not made anymore, the Intel® NUC Kit DE3815TYKHE was a fanless unit if I am not mistaken -> https://www.intel.com/content/www/us/en/support/products/78577/mini-pcs/intel-nuc-kits/intel-nuc-kit... Technical specs here -> https://www.intel.com/content/dam/support/us/en/documents/mini-pcs/nuc-kits/DE3815TYBE_TechProdSpec....
Chaco Canyon supports add-on adapters and this can be used to add features such as this. GO-RITE has built a number of these adapters (which can be found here: https://www.microsatacables.com/intel-nuc-products/chaco-canyon or here: https://www.gorite.com/intel-nuc-products/chaco-canyon). Now, there doesn't seem to be one that foots the bill just yet. Perhaps you should contact GO-RITE and discuss this with them...
The following NUC families have a mini-Toslink jack at the back panel that outputs multi-channel digital audio:
Akasa makes fanless Newton cases for these 3 series of NUCs, and I have one each of NUC7PJYH, NUC6CAYS and NUC5PPYH running fanless and headless in their respective Akasa Newton cases, for purposes including NAA (network audio adapter).