Contrary to the impression you convey (see Nature 509, 533; 2014) biomass-burning cooking technology is advancing steadily. Stoves are now more efficient and emit much less smoke, and will remain popular as long as users can access biomass, such as wood and dung, at zero direct cost. Efforts must therefore continue to make clean fuels available and available fuels clean.
In trials of new types of biomass-burning stove — including the trial covered by the 2012 report you mention — one factor contributing to the apparent negative outcome is promoters' use of the term 'improved' to market new stoves, often without justification. This has led to the conclusion that the 'improvements' have not worked. Genuine improvements can stem only from systematic testing and assessment. Moreover, randomized controlled trials of health interventions need to follow strict criteria (see, for example, K. R. Smith et al. Lancet 378, 1717–1726; 2011).
This autumn, the Global Alliance for Clean Cookstoves in Washington DC and ISO, the International Organization for Standardization, are due to finalize the first health-based emissions standards for biomass stoves. These are informed by the World Health Organization's upcoming Indoor Air Quality Guidelines. No longer will funders, non-governmental organizations, the private sector, the media and researchers have to rely on vague and unsubstantiated descriptors to judge stove performance.