Nothing about the POWER8 or IBM's process technology implies unbackdoored. I can't inspect the factories, or their supply chain, or the HDL they used, or the tools that processed the HDL. The only thing more "open" about POWER8 is firmware in some deployments, and maybe licensing the ISA (if you have enough clout/money to join the foundation, I can't find any licensing information at all). RISC-V is more interesting in every way, with respect to openness.