This isn’t the perfect solution but I unscheduled a show I wanted to give a high priority and then rescheduled it. As I understand things that gives it a higher priority because it was recently scheduled.
I believe from my experience that priority is given to the show that starts first and if all the shows start at the same time the shows that were added most recently get higher priority.
Alternatively you could set the priority shows to start just a few seconds early or low priority shows a few seconds late using this hack if you are tech savvy.
I don’t think either solution really makes up for a simple priority menu implemented by Tablo. I really wish they would do that but I don’t have that many conflicts.