This is something that has been suggested already many times and is a -1 from me for the following reasons.
I will give my opinion as Administrator of PRO, but this is just my own personal one and doesn't necessarily reflect the one of DEVs.
A housing system definitely looks appealing from the player perspective, but personally (imho) speaking it looks a really big waste of time from the Staff one and also don't think it would be something really needed or wanted by players.
Introduction
First of all, it's important to mention that to have a good result we should consider a complete housing system and not a half-baked one with no customization or similar as that would have no sense.
I will anyway do comments about both the issues in the complete and half baked one,.
It' important to say that the way maps/tiles (floor, furniture, trees, etc to make you understand) and NPCs works in a way that doesn't allow a housing system in this moment.
Maps, for the one not being aware of it, are in the first place manually created through the usage of an external client. Also, a single furniture is divided in different parts that are to be placed in different layers.
For example a tree is generally divided in 3/4+ parts where each part is to be placed in 4 different layers manually; sometimes the layers used are different even for the same tile if you need to achieve different results (the water/ground under the water on maps is actually a good example, but not the only one).
[STAFF SIDE] The issues with the Housing System
Giving what has been said above, it is currently not possible to allow a player to manually create a map and manually place a furniture into a map or in general to customize it. Some of the reasons are:
DEVs would need:
A lot of code-changes and also to create an editor inside the official client of PRO to manage players to place NPC/Tiles(Furniture, floor etc)
Need to create an interface that allow users to create a list of allowed people that can enter a house and a way to automatically update the NPC if you want a player-house and not a guild one.
ART Team would need to work on tiles, but this most likely will require a further rework from DEVs on how tiles works in game and I am not even sure this is possible
CS Team would need to handle the in-game scripting part for what regard all the NPCs. Also NPCs path and rotation are hard-coded value that are customizable by the CS, but this is done through an external editor and this would require an extra work from DEVs again unless you want to have 300 NPC hidden in a map causing lot of lag.
MAP Team, if we go for a half-baked Housing System with templates, will have a huge amount of work to do for those templates.
I am sure that there is many many more and the DEVs can definitely expand and mention even more stuff from their end that would make it even many times more cancer than it looks now.
Do take that each of the above stuff would include the entire team of the mentioned role, and therefore would remove time and work from every other aspect of the game (included the most important one).
[GAME SIDE] The issues with the Housing System
Exactly like the staff side, here on the game side there are as well many issues that I will try to address properly:
Amount of Houses
Housing system lead to the result of giving everyone the possibility to have their house and PRO to have due to that over than 20.000+ houses, and this will be definitely not possible to be handled in a comfortable way. Good to consider that if you want extension, and giving that what you described as "outside garden" is literally a second map, it will be like 40.000. If you want a second floor then that's another map and it will be 60.000+ potential and so on.
"What if we do it only for guilds?" is what some of you will ask, but the answer will be the fact we have Guild Island and that is the main 'guild feature' that should not lose any appealing.
Appealing
What would the house/map contains?
Definitely and absolutely not hunting places as that would open us to many vulnerabilities in terms of botting and similar;
Definitely not money-income sources as that would damage the economy;
Tutors? They are on Guild Island.
If we make just 2-3 basic templates and therefore no customizable, why would someone get one giving what written here above? It would be just a generic random house like anyone you can find around any region.
Conclusion
PRO Absolutely do not need at all a Housing System and would not benefit at all from it (not staff or community).
There are still really really really a lot of things that PRO lacks or need a rework from specific Staff Team (you can find DEVs here) and all of them are things that will objectively have a higher impact on the game and community in terms of benefit and importance.
Guild Island, with some adjustment currently done by Walross (spawns) does everything necessary a Guild needs.
Asking for such a suggestion to be implemented is the same as asking to put everything else (Astrella/Unova and what will come next, New Themed Pokemon and NPC Sprites for stories, all the DEV To-Do list, all the events, all the CS scripting, etc, etc) on a break for a long long time.
I have tried to be as short as possible but to give the minimum of information needed about it, have a good day o/