Well... for the first 15 or so years of my musical "career" I avoided any and all theory (aside from a year of lessons at the start when I was 12 that got my fingers moving the right way but not much else). I just mashed at the strings until something interesting came out then would mash that mashing into my mashed potato brain until it was perfect. I did not want outside influence at all. I did learn other people's material if it REALLY pulled me in so there were definitely influences and I "created" little scales of my own based on that then used them for my leads. Harmonically though I simply did not think about it. It sounded good or it didn't. I'd mash parts into odd compositions (3bars, 7 bars, weird variations interspersed, reversing riffs, whatever). It was chaotic, schizophrenic yet somehow cohesive.
However that was very limiting and writing was very much a chore so I started learning theory. I realized everything I was doing very much fell within traditional theory... but it was just a little twisted. So I wasn't necessarily being "original" per se but the way it was being put together was.
I contemplate often whether I fracked myself by not learning theory earlier or whether it has helped keep things fresh. All I know is writing is a lot easier now and I still have a very hard time figuring out exactly WTF I am doing after a song is written. Basically keys and modes are flying around all over the damned place... like changing every second or so sometimes and when I write I still just through caution to the wind instead of worrying about what is "proper". Still the theory helps when I want to do a solo or write complimentary basslines or am having a hard time finding the right fretboard pattern to splay out for followup riffs or ornamentation.
We have 12 notes to work with which can be viewed as limiting. It becomes even more limiting when we think of diatonic theory even when accessing all 7 modes (and a lot of traditional theory will limit that even further ignore tonal possibilities outside the Major and minor key approach).
This is why I like riff metal or riff based music in general. It's kind of like a melody that the harmony is being forced to follow. You can do a hell of a lot with those 12 notes when you are ignoring everything underneath them and then building up the song around the riffs.
Then add in quirky time changes, bar/beat setups, additional melodies (like solos and vocals over top of riffs, the whole craziness and variations drums/percussion can account for and timbre/instrument/amplification/acoustic choices) then you REALLY start getting into a crazy amount of possibilities.
Look at what is possible with simply a 1 and 0 in physics. It can explain the entire universe and endless possibilities beyond. We as musicians, even simply using the 12 tone chromatic scale, have infinitely more to work with.
So yes... it most certainly has NOT "all been done" and we are currently experiencing an EXPLOSION of new technologies that are making almost ANYTHING possible.
The only limitations to us as musicians in 2014 are the ones we impose on ourselves.
Cheers.