In Revit 2023 you cannot select two (or more) elements, then hit dimension and end up with a dimension line dimensioning your selection.
The idea would be to allow that. Revit could even determine which dimension to use depending on whether the selected entities are parallel to one another or form an angle. If selected element were just a single element the dimension could be an xyz coordinate.
This would be similar to the tag-all feature - tag only selected elements.