Thanks for coming up with this interesting idea and article.
At this point, I guess it is important to stress that, on the one hand, we create better conditions for animal welfare, reduce stress, cannibalism, some metabolic problems, including carcass alterations, leg problems, wooden breast syndrome (in the case of broilers). On the other hand, we significantly increase the risk of bacterial (salmonella) and viral (influenza) infection diseases, given that the birds will be exposed to all the challenges of the environment, including contact with insects, wild birds and wild animals. Due to the constant contact with the soil, there is a much greater probability of parasitic infections, which will force the greater use of anthelmintics.
However, for small properties it is a system to be considered.