This is actually an idea that I came up with a little less than two years ago -- when I was Governor, I spitballed with Yankee about the possibility of having organized Presidential primaries. So, I'll butt in to offer my take:
Primaries are an interesting concept, but when you keep in mind that parties generally don't have more than one or two dozen active members, some primaries could have only a handful of voters. In addition, I think that IRL America's convention system is a pretty outdated model that takes power out of the hands of the actual voters, and the current system (in which the party's actual voters are the final arbiters of nominees) is more than adequate.
If Atlasia had hundreds or even thousands of active players in all sorts of different states, and you could get a few dozen people voting in each regional primary, maybe the non-convention part of this would be a good idea. With these things, simpler is usually better.
