[unsafecast]

Of course it does - endianness interferes with any sort of numeric literal. Doesn't matter if it's hex, decimal, underscored, whatever.

[Wildgoose]

I think you are missing the point - there is no endianness in normal written text, (or code), but there is endianness when that is translated to an actual number - what order are those bytes intended to be used in?

(Given they have been listed separately rather than as a single number).

[unsafecast]

What order are the bytes in 0xabcd intended to be used in? I don't see how making it 0x[ab, cd] would be ambiguous, it's the same assumption of reading left to right.