I'm sure this has been discussed plenty before (thus the phrasing of the title) but my google-fu is not cooperating today and I have yet to find anything quite like this idea.
The idea--the suggestion for the programmers--is that we should have stables available for our housing.
Not merely some houses that already come with rooms that are meant to resemble stables (which already exist), not players putting together things to resemble a stable (though player-customized stables will still work, as per my next paragraph), but an actual furnishing option that basically functions as a container that displays the contents, with those "contents" being the animals themselves.
The size of the stables (and by extension the price) could determine how many animals you can fit in one and how much room they have to move around (pets already have an AI that lets them wander a bit in the outside world, I see no good reason why they--or mounts--should be stuck in the exact same spot you put them in when placing them in homes). Depending on programming ability there might be an additional option to "furnish" a stable via whatever decoration would resemble food or beds (piles of hay, for instance), or else the "container" could already have beds and piles of straw as part of its built-in appearance.
Custom-built stables would certainly work for this as well--would probably work better given the request to furnish them with "food" and beds--as long as the animals are still given an AI that lets them wander whatever area the player blocks off for the purpose. Again, mounts and pets alike; as far as aesthetics is concerned I really don't like seeing any of my animals just standing in one spot and never moving until I personally relocate them, I want them to be able to move on their own.
And to refer to those who want a stablemaster for their homes... my idea focuses purely on the aesthetics, especially the part about them being able to wander. A stablemaster to improve training could be useful but that's not what this is about.