This question comes up from time to time and usually there is no direct answer.
A few years ago someone(vengeance?) posted a long list of things thats they planned to implant and what direction PS would take. Sadly i couldn't find that post.
Some of the things mentioned there are completely opposite to what we have now.
One thing is remember was narrow street structure for the sake of performance. Hydlaa changed from MB to CB in exactly the opposite direction, giving wider views(and messing up proportion).
It seems to me that the goals change from year to year, so even if the developers gave you a list of what they want to achieve, the end result would be something different.
Some changes are most probably due to technology evolution, designers realize that they can do now what seemed impossible to achieve before... and sometimes they realize they just can't meet such or such requirement. It's funny what you say about the street structure and maybe it illustrates that perfectly, when Boonet saw the new Hydlaa layout at the beginning of CB, he said that it was how it was originally meant to be. Perhaps it was too difficult to achieve, although I think that at the beginning of MB the mesh occlusion was not already part of the Crystal Space engine, yet the client performances were quite good on a reasonably good computer (unless someone was messing with the collision system - I won't give names

). The city was meant to be bigger anyway so it must have been a good decision to flatten it somewhat at the time, knowing they could finally count on occlusion culling to reduce the processing. I'm sure that people who were present at the time of AB could comment further on that.
We have to admit that, even if there have been some turns in the implementation, the setting as it was originally decided (or what we know of it at least) has been pretty much respected by Talad and his team. It's sad the old Planeshift archive site is not available anymore (maybe with the
Way Back engine?), because you could see that the setting was already there at the time of the 2D version. That's anecdotal, but you could also do a web-based quest on this site!

In a 2001 document (Luca Pancallo, Jan Willy Sandbraaten, Wouter Wijngaards;
Requirements of the Persistent Multiplayer World; June 20, 2001), the Planeshift required features were described quite precisely and the evolution of the game seems to follow those lines. For example you could read (this part was also divulged in the news little before CB was made public, 3 years and a half later):
"When a character dies, his body lays on the ground, lifeless. No one can touch the body since it’s surrounded by a magic death aura.
The spirit separates from the body and asks to the gods to be resurrected. The gods normally take all non-magical items and money as a fee, leaving to the character all magical items and only a small amount of gold. Then the gods transfer the spirit of the character to the Realm of Death where he must accomplish a quest to come back to life. The difficulty of the quest can be related to the level and alignment of the character. In the Death Realm the player gets no experience points.
In the realm of death everything is dim and shadow and the spirits of the dead cannot die again, they may be knocked out but never die no matter how badly they are wounded.
After solving the quest he can ask the gods to be teleported back in the place where he dies or to the nearest temple."
Most of the famous buildings and characters in Hydlaa were already described in another document in December 2000 (Luca Pancallo, Martin Allander;
Yliakum, First Level; December 27, 2000), in which Jayose was already using falka lamps, unaware of the trouble it would cause him, and in which Harnquist was already sharpening weapons (hum, and it was a Kran...).
But Kada's tavern was not mentioned, it must have taken that much to bend Talad's original plans

The same goes for the magic system, which was already in the works in 1997 apparently. The six ways, glyphs and spells were already specified in minute details in 2001 (and probably much earlier) as we know them now - the implemented part anyway.
And Ojaveda too, in an old but undated document (probably 2000-2001) the dsars were already described (the "Tavern of Trouble" changed its name although the new one depicts the same idea):
Dsar Akkaio: this small dsar is located on the main road that lead to the temple of Laanx and to the city. Due to the privileged position, the shops and taverns in this dsar are very popular.
The “Tavern of Trouble” is a popular meeting point of travelers and a place where the two ylian merchants, Arrehnius e Rotrari Mendoki, sell their goods. This tavern can accommodate more than 100 people at the same time and is famous for the enkidukai beer, produced in the fields near the village and brewed in a traditional way. This drink is exported in all other levels in limited quantities and due to this is quite expensive and rare. The owner of the tavern is the huge Brado (at least compared to enkidukai sizes), famous for his skill to stop any brawl by himself and for his loud and deep voice. In the back of the tavern, there are some rooms for gambling, prohibited by the laws but tolerated by the leader of the village.
Located in the west side of the main road there’s the Trasòk Weapon Shop, the most respected weapon smith in Ojaveda. Twenty-two people work in the shop and ten of them are dwarf of the hammerwielder clan. Here you can find the best weapons of Ojaveda, particularly axes, very handly and well balanced.
Another interesting shop is the one of Vladovic. Vladovic is an old Xacha, considered one of the wisest person in the village. His profession, in addition to the one of giving good advice, is the herbalist. This lively old man has a great knowledge of plants and he’s able to prepare healing potions and ointments to remove wounds and diseases. He provides also powerful poisons to the guards used to keep at bay the monsters of the Stone Labyrinths.
Compared to what is public now, there is still plenty of material for the magic rules, Ojaveda, some quests, plus everything that must have been added since then. That probably doesn't answer the original question since there is no reason to believe everything should be implemented in order to declare version 1.0 err, gold, but it tells that there has been a road for quite a while and that the development team is still on it.