Unfortunately 50 years after the death of the author (or 50 years after publication for corporate owned works) has been locked in as a minimum term through international treaties, so it'll be somewhat hard to lower it beyond that, but many countries (including the US) enforce much longer terms, so that would be a first lever that could be applied quickly.
Maybe countries could could also establish an exception for out of print books offered to the public for free, or a general "library exemption" for public archives after a certain number of years?
I'm sure one of the AI companies would be willing to host a LibGen style library as a PR measure if legally allowed (with sign up required for rate limiting and as an extra benefit for the company to get daily active users).