Honestly, I'm pretty amazed to hear some of this community is aware of WebTV for Dreamcast, or just WebTV in general at all, and are interested in seeing it looked further into. Gives me a bit more hope that something can be made out of this soon.
In terms of news concerning documenting/preserving WebTV DC content, I did finally get to uploading a TellyScript designed for the Dreamcast version of WebTV onto my wiki's content archive (TellyScripts are essentially more powerful dialing configs that instruct WebTV clients how to dial, which are downloaded from pre-registration servers that WebTV clients connect to when no TellyScript is already downloaded or if it happens to not be usable anymore). IDK its exact origins but I think I got it from a Git repo for someone else's proof-of-concept WTVP server, and the TellyScript might've been obtained from MattMan's full private WebTV server. All I'm concerned about right now is that it's finally preserved outside of my hard drive, and it gets to see another day. Anyway, the DC TellyScript compared to ones made for dedicated WebTV hardware is
much smaller, and when I asked former WebTV employee Andy McFadden about it, I learned that most of the TellyScript functionality was baked into the GD-ROM and the DC TellyScripts were redesigned to simply call higher-level functions directly from the software. The official reason for doing this was that the Dreamcast has way less NVRAM storage to accommodate the (usually 12KB) size of original TellyScripts. According to an internal "Greater Scroll of Dialing Wisdom" document written for WebTV staff, original WebTV boxes had 16KB allocated for TellyScript storage, while the Dreamcast would only allow 2KB to be used for this purpose. On the topic of TellyScripts, Fadden has also just written code a day ago that
decompresses and decompiles original TellyScripts into C-like pseudocode, which while not perfect, is a massive step in the right direction when it comes to WebTV. I'll continue to keep you guys updated when more breakthroughs are made.
P.S.: IDK how common WebTV Dreamcast discs are in actual Japanese stores, but finding WebTV Dreamcast discs for sale online is relatively easy on eBay and Yahoo! Auctions Japan, albeit new listings don't pop up often, and some listings ask for a bit too much for the software and some copies show some wear or damage. Otherwise, just stay vigilant with the listings and you might get a good deal.