I think this would appeal to many more people if it were a machine the size of a Taig or Sherline. Although some of the concepts are transferable, there will be a lot of issues in building something this size which would not be relevant to a smaller machine.

Are there really that many people with the kind of space for this and the items it produces who want to build their own 5 axis mill?

I also wonder how many people need the parts produced by a 5 axis machine with its enormously greater hardware and software complexity. In most cases you could design what you need to be built on a 3 axis machine and assemble it. For under $2000, you can have a lot of fun by buying/assembling a Taig CNC mill with a 4th axis. 2 1/2D and 3D raster software is not crazy expensive or complicated.