UPDATE: There is a temporary fix
I worked with Natalie from Goto support and we created a work around. First we created in our main schedule under holidays each of the upcoming holidays. Then we created a separate schedule called Thanksgiving, and another called Christmas party and another called Christmas. In each of these additional schedules we created future events such as Christmas 24, 25, 26 etc. and recorded that we would be closed on those dates. Then in the dial plan, we linked the first holiday schedules "Thanksgiving" to the "When on holiday" tab in our main schedule. Next we linked the next Holiday Christmas party schedule to the Thanksgiving Holiday Christmas schedule under the "When closed" tab, and linked the Christmas Holiday schedule to Christmas Party schedule in the "when closed" tab. What this does is it knows all the dates in the main schedule of when the holidays happen, and it links those dates to the first holiday schedule and if those dates are not recognized because it's not that holiday it considers that schedule to be closed and it will go to the next schedule and so on until it finds the right one and it will play that audio clip. You can see that we have a specific audio clip for each holiday, it would be even easier if you had one holiday clip that was generic, but we like to be specific. Hope that helps!
FOR THE PROGRAMERS:
After going through this fix I think the easiest and simplistic fix would be to be able to add a column in the Schedule itself under holiday to add a sound clip. That way all the information is right there in one easy spot (The Holiday, Date & Time, What sound clip to play if desired). The second improvement would be to be able to add more than one date to each Holiday. For example: 12/25/24, 12/25/25 etc or if possible every Dec 25th. Thanksgiving is a little more tricky since it falls on the last Thursday of November. Maybe that's in the next AI update?