What audio product needs to be invented? I'll start with an easy one: truly wireless speakers. That would be great; all they need to do is figure out how to beam enough power to speakers to drive their internal amplifiers. I doubt that's going to happen anytime soon.
Maybe an app that converts crappy-sounding iTunes to true 24-bit/96kHz files, or Bluetooth audio that sounds decent. How about surround-sound headphones to listen to all of the great music recorded in surround? Oh right, first we'd need great-sounding music surround recordings.
How about a great-sounding subwoofer that doesn't transmit bass to the rooms below, above, or to the sides of the room the sub is in? That would be great.
High-resolution portable players with TBs of storage? I guess, but I don't really understand the desire to play high-quality audio in the noisy world--in cars, buses, planes, trains, offices. Resolution mostly refers to the music's quiet details, like when the guitarist's last note dissolves into silence, the subtle sense of place you hear from good live recordings, that sort of thing. You'll never hear that stuff in your car or on a plane. High-resolution audio is something you can only really appreciate at home.
Most of all, I'd love a speaker that perfectly re-creates the sound of live music. We'd also need a perfect amplifier that doesn't add or take anything away from the signal, but despite all the advances in playback technology, recorded music just keeps getting worse and worse. Older recordings were imperfect, but they sounded considerably more realistic than most of today's hyper-compressed and processed releases. So by the time the perfect speaker is finally unveiled, recorded music will probably be even more disconnected from the sound of human beings playing instruments or singers singing. Even perfect speakers might not be able to correct crappy-sounding recordings.
What audio products have yet to be invented? Share your thoughts in the comments section.