I think negative scanners have been at 4200 DPI for quite a few years, but for a larger flat surface? Maybe to scan high quality prints and artwork, but that kind of stuff I expect from businesses and museums, law enforcement and such. You'll get individual micro-grains of lead from lead pencils showing up.

(As a non-business non-professional end user I need 4200 DPI and more from negatives, but I'm a special case. A nut case when it comes to it.)