Very good idea Belle.
I've always felt so sorry for my pony, my white horse, and for my Arabian, they just follow me around but they are never used. Animals like to serve their owners, they want to be ride.
And the sets could gain some more points for the jobs an all-round setting can't do. I still like to be able to do all jobs, I really like not to have to re-spec for doing some job for a quest.
Specially when I think of that it costs me real money to re-spec for quest jobs where the output is so poor as we have seen them. I think of the high level quests like the Circus quest and the Hope dies Last quest where the reward is a box where we risk to get crappy items. Getting a fancy cotton shirt as I got from my Circus quest box where I spent real money, money I could have spent on other things, to be able to finish it, that is simply not Ok. And now the latest change in the reward for finishing the Hope dies Last quest where the nice named pants were exchanged with a pair of fancy army pants, a pair I already have, where the box is the only other alternative and I risk to get some other level 20-something item from it.
Adding the horses to the sets so an all-round build is possible would be nice.