You already can get part of the way there by desigining your own FPGA board (I believe there are some Lattice chips with an open-source toolchain, otherwise the toolchain is closed). On top of that you can run your RISC-V CPU and the other components you need to create a working SoC, with all the RTL under your control. Custom silicon in our hands would be quite a stretch though.
Yes indeed - the open source toolchain (yosys, nextpnr and GHDL for VHDL support) isn't 100% "there" yet, but it is good enough to use for real projects as long as you keep the limitations in mind. It supports several different FPGA families now, with Lattice ICE40 (project icestorm) and Lattice ECP5 (project trellis) being pretty mature, and (somewhat more experimentally) project XRay for Xilinx series 7 and project Mistral for Cyclone V - and others too.
My own CPU (EightThirtyTwo) and SoC project (SDRAM, video, sound, interrupts, uart) can be built for ECP5 using Yosys and friends, as well as for a number Altera/Intel FPGAs using the proprietary Quartus.
Glad to see that open toolchain support is improving, as FPGAs on modern nodes have the potential to run truly open hardware with reasonable performance. When I did my last FPGA project I was basically forced to use the Xilinx and Altera flows from start to finish. I work in the silicon industry and it's sad that everything is proprietary (compared to the number of open-source frameworks and tools on the software side).
This is a +1 to all those that commented below/above (I never know where these will get rendered). I had no idea you could already get pretty far. That's awesome.
