Things that would be great

This is a section for thing that I have thought that would be great in the game, but at the same time would be hard or even impossible to accomplish.

Weather, time of day, seasons
In most MMORPGs the weather is just a particle effect, it doesn't change anything. But in car game, it should affect the grip, change the way different tyres handle on different surface, reduce visibility, maybe it would even mean that the cars would have wipers, so it's extremely hard to accomplish.
Same thing with time of day, many MMOs have day-night cycle, but in most of them, game world doesn't even get decently dark during nights. What this game would need are really dark nights, which would mean that vehicles need to have have lights, which in turn would make the game engine extremely heavy, so I propably have to ditch the idea about day-night cycle.
Including seasons would be great, during winter some areas would become snowy, roads would be very slippery. Problems are exactly same as with the weather.

Player owned areas or bases
It would be really great to have some sort of player owned areas or even community owned areas. I've given this idea a lot of thought, but it's really hard to implement. Few Ideas I've had so far:
1) Player housing, players could buy an apartment in the cities. This would actually be quite easy to create, instanced apartments inside buildings in cities.
2) By off road exploring, you could find a place where you can build player owned base, if you keep the base long enough, there would appear a road connecting the base to the main road network. You could build defensive buildings to the base and if someone would like to take the spot from you, they would have to destroy your base first.
3) Players could capture raider bases for themselves. Otherwise same rules as in no.2

Problem with 2 and 3 is that the amount of those bases would be limited, so it would be possible to one guild to own them all, of course, this could be prevented by limiting the number of bases a single guild can own.