The new missile that was tested in Kapustin Yar on October 24, 2012 remains a bit of a mystery, but probably not for long. As I was going through my old notes, I discovered that the commander of the Rocket Forces, Sergei Karakayev actually described the new missile in some detail in his December 2011 interview.
He mentioned a development of a new "medium-class" solid-propellant missile "with a new type of combat payload" that will be deployed on mobile launchers as well as in silos. Karakayev said that the new missile is build "on the basis of the technical solutions implemented during the development of the Yars missile." He also said that deployment of the new missile is expected to begin in 2015.
So, everything suggests that it is an evolutionary development of the Topol-M/Yars line (as it was suggested at the time of the first failed launch attempt in September 2011). The "medium-class" reference could suggests that the new missile is somewhat heavier than Topol-M/Yars, although probably not much - it should still be light enough for a mobile launcher. The initial reports suggested that the new missile uses the same first stage as Yars (that explains Karakayev's "Yars technology" reference), so the difference is probably in larger upper stages. The missile could probably fit in the same launch canister (but it's just a guess). The "new combat payload" part explains the launch from Kapustin Yar to Sary-Shagan. I hope that we'll hear more about the new missile soon.