Trying to understand the ideas behind the Zion Plat description, given what is generally known about farming in the 1815s---see Daniel W. Howe, What hath God Wrought, Cambridge University Press (2007), Chapter I The Continental Setting, Section.2---or the description of Joseph Smith Sr as a farmer, is now always easy.
For the purposes of this discussion, the question of what happened to the various temples is not very interesting, though this was indubitably one of the key issues for the Mormons themselves. The focus extends to the basic infrastructure for the individual lots and houses.
The agricultural society of the times was a single-family unit of the husband and farmer and the wife, plus their children, possibly some old or unmarried relatives, and/or borders.
That unit has its house on the 2000 m2 plot that each family receives, with the tree grove in the front, the house 25 feet away from the street, and the garden in the back. Since the garden is the main source of the fruits and if at all vegetables that the family will consume, it make sense to have it close to the house. It is possible that the grove was supposed to include fruit trees as well. The garden would most likely also include a privy and the well, if the lot has one, though the commentary does not make that clear. It is also possible that workshops would be located here, such the grist mills, carding machines or the cooper shop that Joseph Smith Jr worked in when he lived on the Smith family farm on the Manchester/Palmyra line.
What is more puzzling is that the stables and the barns have been moved out and placed into the south (not, as sometimes said, the north and the south, just the south). This effectively means that the main units of transportation and mobility, the horse and the carriage or buggy are away from the house. Not only does this make transportation difficult, as the horses are possibly up to 1.41 miles away from the house (in a square plat, the max distance is the diagonal of the plat). The farmland, on the other hand, is supposed to be up north and tended by the agriculturalists. This means that the farmland is even farther than the house from the animal power that assists in the plowing.
There are some ameliorating factors to the arrangement of living. While in slightly different Indian configurations, such as the Old Southwest, a similar agglomeration of horses would have provided a very enticing target for Apaches and Comanches, the centralization also simplified supervision or even guard duties. The description says nothing about that, but it could have been the intent. Furthermore, thinking back to the anecdote of Joseph Smith Jr and Emma borrowing the wagon from Joseph Knight Sr for retrieving the golden plates of the Book of Mormon in Lucy Mack Smith's history, there was an expectation that the animals would be roaming the forest and that a considerable animal hunt might be required before being able to depart (EMD I.B.5, p.328). In such a context, the long distance could feel acceptable. Furthermore, the requirement that stables and barns are to be outside of the settlement does not prohibit one from leaving a horse in the garden over night, at least not as far as we can tell.
Another puzzlement is the absence of any locale for manufacturing, industry or shops. Admittedly, in the context of a city full of Saints, it might be unnecessary to export anything from elsewhere, and the majority of the workshops at least could fit into the yard, though that would probably not be so for the steel mills and brickyards. But taverns, general stores and specialist shops like pharmacies were well known; the Smiths had operated the one in Palmyra and the other in Kirtland, Ohio, and they were acquainted with Dr Robinson's pharmacy from Palmyra. It is unclear where they were supposed to go.
Finally, there is also no other form of connection to the economy of the larger unit, no postal roads or wharfs on a river or similar. The absence of water in the general case is a bit suspicious, but maybe they were expecting to have no problems with well-digging (as was apparently the case for Palmyra and Macedon).