Nice find!
I guess someone finally managed to coax the kernel sources out of them. Still nothing on the download page, so I guess you got to reach out to them yourself if you'd like a copy.
Are you on the beta firmware that got upgraded to kernel 4.19 Nathan? Wouldn't have high expectations of CAKE being enabled, but at least you won't have to backport.
Either way the software on those things are a disappointment, so if I ever get one it'll be to run OpenWrt on (or just plain Alpine/Debian or similar).