Because it's coming up and she thinks it's appropriate, Hermione designates that Martin Luther King Jr. Day will become Magical Equality Day as well. It's as close as a relevant holiday she can find, and she doesn't want to delay. Winky is ready with an aerosol form of the freeing potion to free House Elves bound to families with, and Neville and Luna are ready with massive charmed hoses to free the vast numbers of elves at Hogwarts and at the Ministry.