Compared to San Andreas the GTA 5 is massive and even when the gta server has 700+ players active the map feels incredibly empty outside of the businesses which serve as hubs to find RP.
It would be cool if the map started off heavily restricted as far as support for interiors, businesses and homes then expanded as neighborhoods filled. This means we would have a busy street with several businesses open on it all the time as opposed to random things scattered all across the massive map.
However I am not saying that the entire server should be restricted to a tiny area. I mean several different points on the map serving as hubs for communities to form around.
For example the hood areas would focus on filling the houses around the davis and the businesses around the clothing store.
Davis
-black/latino gangs
Vespucci
-mobs
-legal rpers
Vinewood
-mobs; jews, italians
Downtown
-lspd
-offices; law firms, doctors
County
-sherriff
-gangs; bikers, trailer trash, etc
None of the groups above are restricted to those areas but just an example of the types of factions people like to play and the areas they tend to open around. Just start off with an area for each type of faction so everyone can be close together and actual run into players while walking around their neighborhood as opposed to all RP taking place in houses.
When I moved from NGRP to LSRP this was what I immediately noticed back in the day. Even though NGRP had slightly more players at the time that I switched over it felt like much less because you had players spread all throughout LS, San Fierro, Tierra Robada and the county. Where as in LS-RP you could walk through Ganton/Idlewood and even East LS and run into people posted on every block.
Even though people look down upon the Mall and Idlestacks I think having those known areas where people gravitate to when their friends or faction are offline or at random hours in the night are important.
RP requires another person, keeping everyone close together would make the game seem 100x more alive.