Thinking about this topic some more, it seems hard to gain the critical-mass of contributors for such an open-source tool.
Place-and-route for example, requires a very specific set of knowledge in both optimization (comp-sci), and hardware (electrical). Most of the people who have these skill sets are probably already employed by the major FPGA vendors and under NDA to not contribute to such an open-source tool. I've seen this first-hand having been in the academic space of FPGA research. New masters and phd grads typically go straight to Xilinx or Altera. And without really really good place-and-route, you won't have a competitive tool.
I'm not sure how you would solve this problem.