Yes please!
My own use case for this is UTF-16 strings in WebAssembly, parts of which are statically known at compile time, those are HTML element names, i.e. <div>, <input> etc. Other parts come from the browser's JavaScript environment, which uses UTF-16 instead of UTF-8, the actual elements content to be rendered. In the end I only need to concatenate them all and feed back to the JavaScript environment.
String is just too heavy for this, especially with UTF-16 <-> UTF-8 re-encoding back and forth. I'd rather operate on this as a byte string, but retain the ability to conveniently specify parts of that final rendered string at compile-time as UTF-16 bytes. I think what's described here would fit well, if only there's a way to specify how exactly byte literals are encoded?
Something like include_bytes or some other way to specify byte literals would be very handy. Currently available array literals just aren't good enough for that.