Since 2-seater boats were added in 1.9, why not have something similar for land?
Horses will be able to hold 2 players / mobs, (possibly at the cost of a slight speed reduction). Just like in boats, the second player riding will not be able to control, but when the driver dismounts, the second is now in control.
Ways to achieve:
A new, craftable saddle made from two saddles (or maybe one saddle and an extra leather?) to replace the current saddle.
A new slot in the horse's inventory that allows placement of another saddle.
Opinions? What do you guys think?