This can't be used in the core as it breaks backwards compatibility and violates the general rule in Sequel that hashes are used for expressions. Currently your code is valid Sequel and results in:
SELECT * FROM movies ORDER BY ((title = asc) AND (year = desc))
Ordering on boolean expressions is supported on most SQL databases, where false generally sorts before true.
A simpler solution to what you want in Sequel is to use a virtual row block:
Note that on ruby 2.0+, you can use the core_refinements extension to enable :year.desc to work in a given file without it having a global effect.
If you wanted to support the ActiveRecord syntax, you'd have to add a new method for it, or you have to add it as an extension that overrode order and related methods to add special handling for hash arguments. Because of the ease of doing this with virtual row blocks, I think it would be better to do this as an external library instead of included with Sequel.