This paper provides a useful overview of the nutritional, and (very briefly) some of the environmental differences between cow’s milk and substitute milks made from plants such as soy, rice, quinoa and oats.  Having described the process of transforming plants into milks it then goes on to conclude that there are important nutritional differences, with cow’s milk generally richer in protein and essential micronutrients.  It notes, however, that the GHG footprint non-dairy substitutes tends to be lower. It concludes:

The launch of the new vegetarian alternative to the meatballs – grönsaksbullar - is what Ikea calls “the first step to include a wider variety of healthier and more sustainable food choices”.

This video portrays the work of Beyond Meat, a company focusing on creating plant-based meat. Their "chicken" and "ground beef" comes from a soy-protein-based hamburger patty.

A decline in meat production combined with further increase in demand could spur businesses to look for alternative food protein sources, said Media Eghbal, head of countries analysis at Euromonitor International when being interviewed by the Food navigator.  

This research from Wageningen University focuses on biotechnology and cultured meat. The same technology that is starting to be used to create new organs from stem cells, could in principle be used to produce meat. 

FCRN network member Hannah Tuomisto has co-authored a life cycle analysis of (hypothetical) in-vitro meat production here: Tuomisto H L, Teixeira de Mattos M J (2011) Environmental Impacts of Cultured Meat Production. Environ. Sci. Technol. dx.doi.org/10.1021/es200130u 

Bill Gates seems to have entered into the meat question.  In his view it is simply not possible to feed 9 billion people on a high meat diet and the way forward is therefore the development of artificial meat and eggs.