>and little to no mention of successful third-party mirroring efforts
That's probably because space requirements are huge (tens of terabytes of storage) and it's probably not legal in most jurisdictions (probably none of them). Those two would probably stop most people who are thinking about this.
But let's say you managed to download and host it all and don't give a damn about law (maybe a Tor node?), you'd still have to grapple with bandwidth requirements for hosting such a huge collection of documents (including anti-DDoS provisions). Finally, I don't think the database itself is offered by anyone so you'd have to scrape the DOI data and create the front-end for the website.
So unless you're rich and are willing to throw lots of money at this, I don't think anyone is willing to do it for no financial benefit whatsoever (and a massive downside if you get caught by the long arm of the US DOJ/FBI).
That's probably because space requirements are huge (tens of terabytes of storage) and it's probably not legal in most jurisdictions (probably none of them). Those two would probably stop most people who are thinking about this.
But let's say you managed to download and host it all and don't give a damn about law (maybe a Tor node?), you'd still have to grapple with bandwidth requirements for hosting such a huge collection of documents (including anti-DDoS provisions). Finally, I don't think the database itself is offered by anyone so you'd have to scrape the DOI data and create the front-end for the website.
So unless you're rich and are willing to throw lots of money at this, I don't think anyone is willing to do it for no financial benefit whatsoever (and a massive downside if you get caught by the long arm of the US DOJ/FBI).