Adding screens to the boats would be really expensive. you'd have to add a water-proof power/data bus system to power the boats, which aren't currently powered at all, or provide a battery-based system that can last out a park day, recharge within the limited time available on some days, have the infrastructure to do the recharging on the boats or swap-outs, and a wireless system to provide the data to be displayed. It would add considerable weight to the boats, which have limited draft clearance already.
So now we're talking boat redesign, possibly needing to completely rework the boat channel to be deeper, which might require changing out the pumps that create the current, etc.
All to add what, exactly?
But I can see the idea of adding screens in the "Goodbye" room with the custom characters...
