Cubicle7 released a preview of the upcoming Stars and Scales expansion for soulbound, talking about what’s going to be squeezed into its 50 pages.
https://www.cubicle7games.com/warhammer-age-of-sigmar-soulbound-mysterious-seraphon/
Which is some specific looks at underutilized constellations like The Starherd’s Path and Chotec’s Feather, deep dives on Seraphon history and culture, as well as their thoughts about Soulbound as a nebulous institution. A lot of info designed to be used by GMs writing a campaign based around them, basically! Which also means it’s just going to be a big lore treasure trove in general.
While it doesn’t offer rules for playing Soulbound seraphon, it does give the Saurus Oldblood and Skink Priest as playable archetypes that, like Stormcast, are designed to tag along on adventures without having their souls patched into the group.
It says they’re designed to be played for one shots and then dissapear, but given there’s loads of unique Seraphon talents and spells coming with them, and some endeavors from Champions of Order mention them by name as examples of what you can do on them, it feels kind of like calling them that is just a workaround for whatever weirdness GW is limiting them with, as far as general playable Seraphon go. I doubt there’s any reason not to play them normally
You can also basically make the entire hero roster using those two archetypes anyway, since swapping a skink priests’s Mind stat for its Soul stat creates a Skink Priest/Chief pretty easily, for example.