A progression server implies that a server starts at some predetermined patch and go from there, so it doesn't necessarily have to be the beginning, but I think that makes the most sense. The time between patches is up for debate, but it would be either "real time" (it took about a year from the original to zilart so it would take a year for the next patch in the series to go on the server), "accelerated time" (faster than normal, but at a decided rate), or "player voted" (players decide when they are ready for the next patch). This server would not be something you could transfer to or from because it has a different ruleset more or less, so getting gear doesn't matter in terms of bringing it to live servers.

There aren't a lot of things set in stone and it really depends on what the community is looking for. I personally would like it if the game started at the original launch patch and went at an accelerated pace or player voted. I know I wouldn't want to spend forever in the game before zilart, but it would be cool to experience at least for a short time.