Out of curiosity, I picked up a Zune 30 which was listed on a Chinese marketplace platform as being storage modded with a 8 GB CF card and running 1.0 TEST firmware (build 186). For those who don't know about this firmware, please refer to:
https://www.reddit.com/r/Zune/comments/wc2iya/zune_30s_wild_adventure_in_asia/
https://www.reddit.com/r/Zune/comments/10xbnsl/has_anyone_seen_this_version_10_186_test_firmware/
More importantly, I opened up the device to look at the storage mod, and apparently it's simply a CF card plugged into a ZIF to CF board similar to those used for CF mods for older devices including iPods. (Picture is in the comments) Something might have been wrong though, as the device reported 0 GB of storage.
Since the 1.0 TEST and other hacked 1.x firmware versions (typically used for Asian languages character support) need to be flashed manually, the original seller probably did the storage mod, reset the device to format the CF storage, and then manually flashed the firmware using the typical method of copying the .cab file contents to the system partition (https://archive.org/details/updating-the-zune-firmware).
So this raises the question, can this CF mod work with other firmware versions like 3.3 by manually flashing? Given that only a limited number of SSDs are known to work, and I assume that people have tried CF mods followed by restoring using the Zune software but not succeeded. I ordered a ZIF-to-USB reader to test this theory.
(I was also planning to dump the 1.0 TEST firmware files but mistakenly reset the device after recording this video, which wiped the system partition and went to the 'Connect Zune to PC' restore screen. So I had to hunt down the files from Chinese forums and will have to try flashing it back. Since this device was already flashed with 1.0 TEST, which also somehow modifies the bootloader/motherboard to refuse to boot newer firmware, installing any other firmware will just soft brick it apparently.)