Interesting theory. Should be easy to test.
What hard assets were absorbed by central bankers after the 2008 crash?
I would have just said assets, since small and medium business and family farm foreclosures rarely make the news, but if it's hard assets we're interested in, I'd start with records from auction houses/services during that period.
Below is a short burp from Wiki;
Consequences
While the collapse of large financial institutions was prevented by the bailout of banks by national governments, stock markets still dropped worldwide. In many areas, the housing market also suffered, resulting in evictions, foreclosures, and prolonged unemployment. The crisis played a significant role in the failure of key businesses, declines in consumer wealth estimated in trillions of US dollars, and a downturn in economic activity leading to the Great Recession of 2008–2012 and contributing to the European sovereign-debt crisis.[28][29] The active phase of the crisis, which manifested as a liquidity crisis, can be dated from August 9, 2007, when BNP Paribas terminated withdrawals from three funds citing "a complete evaporation of liquidity".[30]
The bursting of the US housing bubble, which peaked at the end of 2006,[31][32] caused the values of securities tied to US real estate pricing to plummet, damaging financial institutions globally.[33] The financial crisis was triggered by a complex interplay of policies that encouraged home ownership, providing easier access to loans for subprime borrowers; overvaluation of bundled subprime mortgages based on the theory that housing prices would continue to escalate; questionable trading practices on behalf of both buyers and sellers; compensation structures that prioritize short-term deal flow over long-term value creation; and a lack of adequate capital holdings from banks and insurance companies to back the financial commitments they were making.[34][35][36] Questions regarding bank solvency, declines in credit availability, and damaged investor confidence affected global stock markets, where securities suffered large losses during 2008 and early 2009. Economies worldwide slowed during this period, as credit tightened and international trade declined.[37] Governments and central banks responded with unprecedented fiscal stimulus, monetary policy expansion and institutional bailouts.[38] In the US, Congress passed the American Recovery and Reinvestment Act of 2009.
https://en.wikipedia.org/wiki/Financial_crisis_of_2007%E2%80%932008
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Who owns a lot of the rental properties now?
Blackstone is now 'the largest owner of real estate in the world'
https://www.businessinsider.de/blackstone-is-largest-owner-of-real-estate-2015-11/?op=1&r=US&IR=T