"What would this project need to achieve before folks would start switching?" Nothing. This is a full grown set of tools. So it's just a matter of taste. I switched from 3DsMax to Blender. There is nothing missing. The footprint is very small and it is fast (startup time of 2 sec.). Plus developing addons in Python is very easy. Also a lot of professional render engines are having plugins for Blender lately (Vray for example).

Just compare the price of other packages ;)