This is exactly how a committee would design it if none of the participants had actually used an internal domain.
For example, in Google, https://go/foo had "go" as technically a TLD, and the memorable suffix that followed was already part of the path and not the domain name. It made it easy to type or include anywhere, including chats, posters, presentation slides, etc.
If they were to follow this proposal instead, you'd be typing or including https://go.internal/foo , which while more explicit largely defeats the point of the short URL.
This was very common in Windows shops back in the NT and even post-NT4 days to leverage the hostname as the URL (http://exchange, http://sharepoint, and so on).
For example, in Google, https://go/foo had "go" as technically a TLD, and the memorable suffix that followed was already part of the path and not the domain name. It made it easy to type or include anywhere, including chats, posters, presentation slides, etc.
If they were to follow this proposal instead, you'd be typing or including https://go.internal/foo , which while more explicit largely defeats the point of the short URL.