After playing with this today, I guess the best way to do it now might be to set the display order with room between, like 10, 20, 30, 40, 50, 60, 70, 80, 90, etc. so that if you need to add a forum in between, you can use 11, or 21, 22 and not have to reorder every single other forum one by one.
Still would be great to have a way to rearrange them quickly. Already liked the feature suggestion