It's fun how you refer to anything after K&R as "modern C"; since ANSI C was first specified in 1989, this means that any version since then is modern. Great!
I do agree that "immutable" would have been a better name, but I guess that angle hadn't been invented yet. :)
Something, something, get off my lawn? Actually I wasn't getting paid to write C back in 1989, but I definitely did write C in the era when ANSI C wouldn't have been generally accepted.
Immutable variables are a good idea (indeed I agree with Rust's choice to make variables immutable by default), but, they're not constants, and so this is an unnecessary confusion.
I do agree that "immutable" would have been a better name, but I guess that angle hadn't been invented yet. :)