More careful reading of the FAQ indicates that Win10 is only required if you want the Optane module to be configured as a cache for a primary SATA drive. It is apparently possible, though not officially supported, to use an Optane drive as a bootable device (last time I read the FAQ a few months ago, this was not the case ROCK + Intel Optane storage for Kaby Lake NUCs?). In that case a secondary SATA 2.5" drive would be unnecessary (if your Roon database is <16GB). See last item in above FAQ link. It is unclear if the standard Linux NVMe drivers would play well with Optane, but it is possible.
If you already own the NUC7i7BNHX1 and are willing to try a ROCK install, I would be interested to learn the result.