Most serious hardware is not going to be open. I think this is mainly because hardware companies need higher margins, because working with physical things costs money. For most companies that use FPGAs, the custom stuff is the secret sauce, kept under lock and key. Most open source stuff out there is either hobby, or effectively serves as an advertisement for design services.

I'm not that familiar with OCP but certainly driving commodity hardware costs down is a valid object. My interest is more in specialized hardware at the board level. I believe CERN and other high-energy physics labs collaborate on designs, but I've been out of the field for a long time. Much of that sort of hardware doesn't have use in the industry at large; historically speaking, if there is demand, the model has been to spin out a small company to sell equipment to other labs.

The only category of core with what I'd call a big open-source impact is RISC-V processors, as you mentioned above. This is because a small processor is often useful on a non-SoC FPGA. But there were already free-as-in-beer microprocessors available from the FPGA vendors, so RISC-V adoption is really more of a political/philosophical choice.

When people talk about someday having an OSHW scene approaching the vibrancy of the FOSS scene, I'm not so sure there are parallels. People talk about having open tooling, but the existing tooling is already free-as-in-beer (for the device types most people could afford, anyway). The cost of the vendor IPs is already baked into the cost of the device, so you'd still be paying for it. The argument is that open source tools will be easier to use, but I haven't found that to be the case at this point in time.

I think that hardware is just a fundamentally different medium from software, and attracts different kinds of people. It's a comparatively smaller crowd, who tend to be lone wolves. Maybe someday there'll be a critical mass.