From the current discussion I'd propose the following syntax --
simplifying what is allowed and not confusing users with syntax from
(other) programming languages, this takes into account the wish for
simplification *and* Tobias' proposal to use the semicolon as the range
operator (which also is used in date ranges currently).

use angular brackets for inclusive range, use round paranthesis for
exclusive range. Don't use the out-facing (ISO-Notation) angular
bracket, use ";" for ranges so that future implementations may use a
comma for decimal notation (german), e.g.

[1;2.6)
[1;2]
if there is only a single inclusive range we may leave out the brackets
making the syntax resemble the date ranges:
1;2
As in the date-range implementation we may want to allow "to" instead of
";".

For multiple ranges we may use the "or" or a "," for separating ranges
-- note that this time the comma doesn't collide with the numeric ranges
because we make brackets/parantheses mandatory, e.g.

[;0],[1;5] to (7;9),[11;]

Oh, and supporting "and" for intervals will confuse the typical user,
won't it?

What do you think ?

That also would require interval arithmetics, if the user specifies
several overlapping intervals with "or" we should silently join these
(or leave that to the sql engine).

Of course the same syntax should be generalized for date values, too.