Right now the main problem is that we're so short on devs. The Sickle is fairly close to finished, but there are always other bugs that require our attention.
As for the other questions:
The Sickle actually has ranks, though I'm not sure they already show in the release version (You are always addressed by your rank but I completely forgot to actually set the player's rank whenever he gets a promotion).
Both the Rhalâta (if we do the story DLC) and the Sickle can be started and (theoretically) be completed at any point in the game, until the Point Of No Return.
