This syntax is a convenience for lists of integer values since the sequence
of integers is universally known and does not need to be defined. However,
the syntax does not extend well to other lists of discrete values because
they would have to be defined somewhere before the shorthand could be
correctly evaluated. For example, what would the propoer interpretation of
IN LIST (1.0,1.5,2.0,2.5,3.0-5.0,5.5,6.0)
be? We humans might interpret this to include 3.5, 4.0, and 4.5 but I don't
know how the parser would figure that out.

I don't think a syntatic convenience that is so limited in its use is a
good candidate for inclusion in the system.