Getting on and off mounts in TES was a pain in the butt, and because I was more mobile on foot, I never used them. In Oblivion you had Athletics and Acrobatics, plus custom magic spells that could give you lightning-speed. In Skyrim, you had Ethereal Shout (w/e it was called... stopped playing that game long ago), sprinting, etc... you always missed out on things by staying on horseback, and the damn thing would always get in fights it couldn't possibly win. There goes my 1000 gold. 
The only good thing about mounts in Skyrim was that they let you fast travel while loaded down with loot. Of course, if they hadn't removed the Feather spell, that wouldn't be an issue... anyway...
Red Dead Redemption on the other hand, made fantastic use of mounts. Sure you still had to get off the horse to pick up prickly pears and skin animals, but the horses were much faster than Marston could ever hope to be. The lassoing and shooting from horseback mechanics were fantastic... and if a horse died you had the option of just summoning a new one of the same breed (although I usually just walked back to civilization or tried to tame a wild horse due to roleplaying). All in all, a great system... the best I've experienced probably.
As for DAI mounts? Well, tbh nothing I've seen has me excited about them... I'm not a huge fan of the rest of the party disappearing when you get on one, but aside from that I don't have any other details to go on... I'll try to avoid them, most likely, and I doubt they will be particularly useful.