http://i43.photobucket.com/albums/e3...f/MOGHOUSE.jpg
That link is from a diagram I made a while back for FFXI (sadly the idea was shot down due to the PS2 limitations :x) Anywho I figured this would be a decent time to bring it back up but for FFXIV instead. The main room is the same exact size as the one in XI (counted the squares and all). The black spots are places where you cannot place furniture but that can be changed to fit XIV's collision system, the gray areas will become "no furniture" zones once you do a quest or whatnot to gain access to the newer portions of the house.
As far as shops go, sounds cool, but it really doesn't fix the market wards problem it just moves it to a new location, sadly. Also if the houses are all personally instanced then how would they be viewed by other people? (unless there is a zone with everyone's house listed? If so, I think the MW would be easier to find what you are looking for instead of searching countless houses for your items. And for the storage, let us have the Safe AND the Retainer. Limit the retainer's inventory to be a little smaller and give us quests to increase our Safe size (content please don't just hand it to us).
Mail system, yes please; but Moogles play an entirely different roll in XIV than they did in XI, so having them the ushers of the races seems a little off. So maybe instead of a Moogle flying in to drop off mail what about having a mail slot on the front door where every hour (in game) or so letters get pushed through the slot and flutter to the ground in front of the door.
Gardens and decor, of course. It's not your house without personal flair.
Something to make it more unique and different from XI? How about the ability to purchase or do a quest to add on a "crafting room" you can only pick two crafts and it will make a small room that is themed to look like the craft you've selected. You can then use the different objects in the room to help your crafting skill, each having different effects of the crafting process.
For example: Cooking skill is you main craft? Do a quest, get your own personal kitchenette room. You can use the counter-top to speed up (increases the % increase per successful attempt) crafts using the knife. Then you have a stove top that does the same but when you use the skillet tool. And Oh no what's this, your character having a bunch of unsuccessful attempts? Why not head over to the kitchen sink to wash your tools and receive the buff to increase the rate of successful attempts. But most of all make all this QUEST RELATED PLEASE, don't just give us everything, people are screaming for content and this seems like a great way to make some.
Anywho, those are my thoughts. All in all, Housing? Yes please!