SAFAD: It's available publicly when the devs deem it ready. Charter Members get it ahead of everyone else as a reward for their donations to help support Simple Machines.
SoLoGHoST: Strictly speaking, the ability for CMs to download and use RC2 should really be for their own forum, not really to allow use on test forums other than ones they are using themselves ahead of the public release.
I would note that there may well be changes between the preview RC2 and the public RC2 so you are advised to NOT test your mods on it just yet anyway, nor can you mark your mods as RC2 compatible on the mod site at this time.
You can see our position; this is a preview given to our Charter supporters and to see a non Charter Member seemingly having access is normally against the Charter Members rules, especially as we may well see "but he had it..." messages.