Samuel Weiss has posted Into the Breach: The Case for Robust Noncapital Proportionality Review Under State Constitutions (Harvard Civil Rights-Civil Liberties Law Review (CR-CL), Vol. 49, No. 569, 2014) on SSRN.

Here is the abstract:

The Eighth Amendment forbids cruel and unusual punishments. The Supreme Court has found in the Amendment a guarantee that punishment be proportionate to the crime. Although the requirement technically applies equally to all punishment, in practice the Court has used the guarantee strictly to regulate capital punishment — a practice it recently extended to life without parole sentences for juveniles — but has abdicated almost entirely on noncapital sentences.

States have authority to regulate excessive punishment under their state constitutions, but most have chosen to interpret their state proportionality clauses in lockstep with the Eighth Amendment. Even the states that have found greater protection in their constitutions have done so cautiously, striking down only the rare sentence so absurd that the legislature could not possibly have intended the result.