These proposals are simply based on an independent enquiry set up in 2001 after the rejection of stock transfer proposals and chaired by Anne Power. Keith Veness knows this perfectly well and is being deliberately misleading.
The Conservatives dumped the proposals when they took over in 2004, but they have remained part of the Labour party programme in Birmingham.
Devolution was very popular in the late 1980s and achieved substantial improvements in housing management most places it was tried. It does tend to cost a bit more in support services, which is why it subsequently fell out of fashion, but the difference is small. Birmingham with its 65,000 council properties is ideal. A number of its constituencies have over 7500 properties which is more than the average District Council. Not much loss of economies of scale here