This is getting good!
Note that these answers are highly opinionated...
The originality of music is a very good question. All music has inspiration. Musicians generally take popular ideas in music (for example, western music with 12 notes in an octave, a 4/4 time signature) and use what other people have done to create something similar, but to give it a slight twist, to make it unique. Some people don't like doing things similar to what others have done; They actively try to create something new and different to what has already been created, still using other songs as inspiration... just that it is inspiration for what the song should not turn out like... And so musical progress is made.
Sadly, I feel that it is becoming much more difficult to find completely new ideas musically. Take irregular time signatures. People often use different time signatures as a sort of musical statement, to say "I'm being different". However, many people like to try and be different, so we end up with quite a lot of songs and bands that play in mainly irregular time signatures. Other people see that the irregular metre approach to being different has already been done, so they branch out elsewhere, trying out noise and dissonance, fusion genres, new sounds (increasingly electronic), modes and unusual scales. While it will never be impossible to generate a song that is different to another one, the probability is always increasing that it is similar to one that already exists. This is fine when it comes to popular music (pop, rock, electronic, classical). We re-use chord progressions, melodic lines and rhythms all the time. We like it. It's comfortable. At least we still get variation from the combination of lyrics, rhythm, melody, chords, etc. all together. So what I've been trying to say is that popular music will always be self similar due to former songs being used as inspiration and with avant garde and unique music it will steadily grow more difficult to create distinctly different approaches to music. It's kind of like an out-hipstering contest.
I would say that music could definitely be evolved from the simple idea of sounds that we have today and that it already has been in certain ways. I would class certain types of visual art and films in this way. The thing is, the mediums for all three are vastly different, so we've already taken the liberty of classifying these into visual art, films and music, even though they have some unifying aspects of generating certain feelings and catching our interest. It's just the label that makes us see things differently.
Even though I know there's a lot more to this on both sides of the argument, I'm going to stop here because it's late and I've been thinking too much...
Also, some more meta stuff: How subjective or objective do you think music is? Can you be brought up to think music with atonal centres is the catchiest shit ever and hate western music, simply based on the experiences and emotions that you have attached to them while growing up? (There are probably many scientific studies on this, but I've forgotten all of the ones I've read.)
We provide the emotion... music is just the key.
