These are mostly actually impossible right now, but being able to think about things that you want that should be possible and seem completely out of reach is a great technique for finding motivation.
The world is much, much, much bigger and more full than our little brains with our little problems can usually understand. So, some of mine:
1. Live, remote, group music performance. Yeah, latency, blah blah blah. This problem can be solved if you have...
2. Music generation as the standard way music is distributed. Some people love hearing the exact same recorded song played the exact same way over and over again. It bores me. And "live" performances are often musically and sonically inferior. Every musician I know is creative, every note uniquely created and delivered. We should convey that uniqueness in the distribution of the music. Yeah, there are tons of "music that sounds like" projects. Have it be part of the musician's workflow. Get them to trust it.
3. Live noise cancellation for spaces. People love noise cancellation for in ear or over ear headphones, where you have tight control over the sound path and the acoustics. Child's play. Solve it for spaces where you may have undesirable sounds coming from any direction, with unusual acoustics and strange surfaces. A $1000 device that does this makes you $B, because it increases the property value of many spaces by 2 orders of magnitude.
4. Accurate performance reproduction. JFC the state of musical reproduction is so completely absolutely shitty. The chills one experiences being proximate to a virtuoso instrumentalist...even the best tube amp speaker set up does not fool a close listener for more than a few seconds. Is there a Turing-test like name for this? There should be.
5. Instrument/track extraction. We're getting better at this, it's the impossible problem we're closest to solving. But there's still a lot to do.
6. Instrument acquisition. Everyone should be able to acquire skills in an instrument. With all respect to the 10,000 hours theory, we are in the dark ages when it comes to acquisition and skill accumulation. Teaching is terrible and pretty much everybody practices terribly. People learn from watching and doing and participating- we are visual copy paste monkeys. With some combination of robots and visual production and feedback systems and nutrition it should be possible to develop benchmarks for dramatically improved acquisition.
Cheers, great question.