i'm not sure i follow, what does split DNS have to do with DoH? i don't want my internal DNS addresses public, there is no need + security and for some addresses i have different IPs internal vs external.

Browsers send to external provider like google, rather than the network provided server which has the internal addresses (and which may override external addresses for various reasons)

split-dns will never die, it would kill far to many internal corp environments where there is no public DNS entries.