The problem with that is that January 1st is a holiday already like you said. There's nothing on September 22nd but it's wrong time of the year. Juneteenth is the right time of the year to celebrate it but it does not make sense because we are celebrating something that had occured in Texas.
Juneteenth is the holiday in Texas. Perhaps we should call the national holiday "Emancipation Day".
It was only the slaves in the Galveston area who learned the news about the end of the war (and therefore the end of slavery) on June 19, 1865. Slaves elsewhere in Texas would have remained unaware for days or weeks more. The mean old slaveowners wouldn’t let their slaves go on Facebook.