Support for Temporal Relation Predicates first defined in ISO 9075-1:2011 (SQL:2011)
Temporal Comparison/Relation Predicates:
CONTAINS, OVERLAPS, EQUALS, PRECEDES, SUCCEEDS, IMMEDIATELY PRECEDES, and IMMEDIATELY SUCCEEDS
Having these predicates would reduce a lot of the effort and pitfalls involved in writing temporally sensitive queries.
I don't know the formal syntax proposed by ISO, but simply having these predicates can reduce up to four separate and hard-to-read expressions into a single one.
WHERE (dt1start, dt1end) CONTAINS (dt2start, dt2end) -- span dt1 is completely within span dt2
WHERE NOT (dt1start, dt1end) OVERLAPS (dt2start, dt2end) -- no part of span dt1 overlaps span dt2
As an addendum, it'd also be nice if the SQL Server teams would put more priority on keeping SQL Server up to speed with more of the ISO standards. There are a lot of other very nice capabilities that have been put forward but are not supported.