Make typed enums declaration without "as" operator

[dmitryuck]

now we have typed enum declaration like this (from docs):

enum Color as u8 {
    red   // the default start value is 0
    green // the value is automatically incremented to 1
    blue  // the final value is now 2
}

the suggestion do like this, similar to generic struct definition

enum Color[u8] {
    red   // the default start value is 0
    green // the value is automatically incremented to 1
    blue  // the final value is now 2
}

while this operator used in some other cases (import alias, type conversions),
the suggestion is to make using operator as for less aims and make enum declaration shorter

[Wajinn]

Why is using as considered a bad thing? That is not being explained, outside of what looks like personal preference.