extend function should be improved/modified

[Oldes]

Current extend function is defined as:

USAGE:
     EXTEND obj word val

DESCRIPTION:
     Extend an object, map, or block type with word and value pair.
     EXTEND is a function! value.

ARGUMENTS:
     obj           [object! map! block! paren!] Object to extend (modified).
     word          [any-word!]
     val           [any-type!]

While in Red language it is:

USAGE:
     EXTEND obj spec

DESCRIPTION: 
     Extend an object or map value with list of key and value pairs. 
     EXTEND is a native! value.

ARGUMENTS:
     obj          [object! map!] 
     spec         [block! hash! map!] 

REFINEMENTS:
     /case        => Use case-sensitive comparison.

And in Red it is possible to use it for example to merge two maps like:

>> extend #[a: 1 b: 2] #[b: 3 a: 1 c: 4]
== #[
    a: 1
    b: 3
    c: 4
]

I believe that being able to extend a value using a single pair of key and value like it is in Rebol now is also useful, but the key could be defined by refinement so default behaviour would be like in Red. The missing case-sensitivity is also an issue in Rebol!