> So the conspiracy theorist in me believes they may see this archiving as a threat for their current copyrights.
The media industry has had it out for the internet archive for a long time. I don't think they see this collection as a threat any larger than anything else the archive is offering. They've also been endlessly pushing for more and more control over the internet.
They've been largely successful getting ISPs to perform vast amounts of work for them entirely for free and without question. They can force ISPs to permanently disconnect users based on nothing but unproven accusations. ISPs who fail to cut their customers off from the internet risk an endless barrage of massive lawsuits. Courts have so been agreeing with the RIAA that this is acceptable.
They've been able to force ISPs in many countries to censor and block access to online content on demand based on nothing but their assurance that something is infringing. In the US they've had less success with content blocking and blacklists but they keep pushing and pushing.
It's insane how much power they've been able to get already, but they aren't satisfied. I see this attack on the internet archive as just another push for control over online media.
> A certain cord progression or beat or a creative lyric and rhyme long forgotten in this old music could endanger parts of their current music catalog.
The conspiracy theorist in me believes that this is actually a feature for them! Anyone who dares to make music without paying the cartel is forever at risk of having their works challenged for sounding too similar to something else. If you're a musician and don't want to pay up and hand your creative works over to the RIAA you'll be giving up the protection of RIAA lawyers.
Most of the other copyright owners who might sue you are also in the RIAA (or their international equivalents) which can make it easier to reach "an understanding" outside of the court system avoiding expensive lawsuits a struggling independent artist can't afford. The constant threat of having your songs challenged helps them operate as a protection racket and keeps independent artists in a very vulnerable position which drives up membership and discourages competition.