Look for situations where a Seek Predicate can be used because the order of rows remains unchanged.
Adding, Substring, Dividing, Multiplying by constant values (for example, for truncation).
dateadd/datediff for constant values
cast(char(n), SomeDate, 112) (and many other styles)
Some non-deterministic functions (such as date functions with weeks) would also work.
And the performance benefits would be huge! Just have more functions that translate into Seek Predicates, letting them return a "this should be higher / lower" result.