I stumbled across this cool map that displays election law changes in the United States since 2006, put together as part of a class project by Professor Carol Nackenoff at Swarthmore.
I think it relies a bit too heavily on commentary from Brennan Center reports to describe election law changes (scroll over Tennessee for instance), and in the area of early voting, there are definitely some missing entries. It’s still a really nice pilot that could be built on by other scholars.