It maybe just a rumor form that message board "Sa-i " but the way things are moving I started to think this would have to happen sooner of later.
A post to a message board on the Oh! great fansite Sa-i states that episode 10 of the Tenjou Tenge anime (to be broadcast on 3 June 2004) will be titled "Kioku" (Memory) and that that will be the start of the past arc. There's no source sited for the info, though.