Sorry if this is the wrong place for my request!
A thing that would be great not only for hard surface modeling: the option to use the Triangulate modifier to triangulate ngons only and to leave quads alone.
This would make working with Subdivision Surface so much easier as Subdiv cannot be used on geometry with ngons in many cases. Putting the Triangulate modifier before Subdiv destroys all the precious quads, though. This means we need to triangulate parts of the geometry by hand which is bad if you want to keep everything nice and tidy and non-destructive.