The real problem is not about some "filthy rich aging rockers" but saving "primary source material" in posession of the folks paying for it.
To take one huge international company - Universal. They spend tons of money to preserve the masters of Brunswick/Vocalion (teens-early '30s), Decca ('30s- whatever), Verve, Impulse, Dot, etc. Why spend the tens of thousands of dollars to preserve the source material if it "belongs to all".
I do not think "all" will pony up the bucks to do this work.