I think some hearing-aids for people who are severely hearing impaired probably EQ upper mids for intelligibility because there is a lot of information in the upper mids (like distinguishing a "D" sound fom a "T" sound).

However, most people I know tend to like a more laid back treble as they age. Sizzly treble is popular with teenage boys that have the best hearing, and later, they'll want the warm sound of a tube amp with relaxed top end. That same sizzle seems to irritate the old-timers.