The question has been asked on the rail section as to why rail replacement buses don't display where they are going.
I am not sure these displays can be set up by the driver but need a computer to do it and the data delivered to the bus somehow.
So how does it work and could they be made to display relevant stuff for rail replacement buses without loads of hassle?
It is very simple to program them. You just download the relevant software for Hanover or Mobitec (whichever of the manufacturer that makes the LED board) and you can program them to say whatever you want. This does have to be done on a computer. So the driver can not just type anything on the bus. However it is very quick and easy to just add an new destinations on a computer and then use a USB to quickly load the new destinations on to the bus.
Some bus operators will just use the generic "rail replacement bus service" but there are some that have programmed a full range of destinations in to the boards to display so that they can display the destination.
Southdown PSV have even got the automated announcements working for rail replacement bus services on their newer vehicles so some operators are quite good with this sort of thing.
So to answer your question the buses can display the destination fairly easily if the operator programmes the destinations and some do but many operators just do not bother with this.