Some of this has been mentioned by others, but thought I'd chime in.
I've got a few clients that run via computer. Here's what would make my life easier.
Being able to load a whole new schedule in easily. Like others, I know the hacks, but it would make it easier. One client has 3 different 'settings' before/during/after Thanksgiving-Christmas. I've got file named for each, and swap them out as needed, but it would make it easier to simply change the entire schedule at one.
And "If/then" type setting would be nice. I have to schedule a 15-30 minute show (musical) to run every 2 hours, and the rest of the time is static. It'd be kind of nice to set the main start/stop time for the static part, which would run all day, and then be able to schedule the musical shows at the same time, with them having priority. If they ever change the times those shows run, it's going to take a long time to set up the new schedule.
This "If/Then" would have helped on another client this year. Their schedule was such that every night I had 10+ shows scheduled from 6-Midnight. The 'static' times (well, animation only) ran when the music wasn't going. The musical shows in this case varied in length quite a bit, so the scheduling was a bit more complicated.
Actually, when I think about it, in both cases a 'play once' for the computer based shows would have been a HUGE time saver. My guess is that would be in the Show Editor. "Play songs once" then "Filler Sequence"
There have been a few times I wanted to remove more than one scheduled show at a time. This would be nice to have.