I'll nominate the physical appearance of literally every receiver built in the past 35-40 years.
Yesteryear's receivers had a classic look with their gorgeous silver face plate, their beautiful blue or amber backlighting, volume and tuning knobs the size of hockey pucks, the perky VU and signal strength meters, the wooden top and sides, buttons and switches for virtually everything, etc.
However, the look of today's receivers are about as boring as it gets. A dull black face with minimal controls and a bland LED readout for the tuner section.
Come on. How difficult would it really be for manufacturers to put style back into the look of their current receivers on the market? Have their designers never seen a Sansui 9090, a Pioneer 1280 or a Kenwood 7600??