Well heck, we’ve discussed this here for two years. The “shadow inventory” is comprised of all those houses owned by sellers (banks and homeowners alike) who’d like to sell but who have held their property off the market while sales were in the toilet. Sales pick up and these sellers see their chance to unload their homes.
I am afraid the housing market rebound will be slow and torturous.
If by rebound, you mean return to previous levels, it will never happen. Not in this life time. Housing is a function of income (primarily) and income will be under stress forever, in both the number employed (or never to be employed again) and the average compensation level of the employed.