Are there fully open-source ASICs?
Short answer: No. It is not a precedent.


There are plenty of Open Source RTLs out there. OpenCores and OpenSPARC are examples, but I know of international academic projects that at the very least were attempting this since the 1990's, almost since the invention of Verilog and before the concept of OpenSource was widespread. The project you pointed to seems no different.
Unless you are actually talking of making your own hobby foundry and you actually consider this foundry (and Arduino) "OpenSource" (instead of OpenHardware) you cannot have open source ASICs. ASICs are physical things that are quite expensive to make.
A group of people can organize together get an existing OpenSource RTL and combine it with an Open Cell Library (like this "fictional" one, or this one that people actually use) and use a fab (nearly all fabs like XFAB or TSMC offer this service) to contract a Multi-Project wafer run for $5000 or so that would be fully "OpenSource" free of all proprietary elements (assuming that you can actually avoid the specific requirements of that Foundry's process and that you did not leave any mistakes in your design).
But guess what. An academic collaboration called MOSIS that is now a stand-alone company has been doing this for more than 30 years. Together with NCSU you can actually have a full PDK that would allow you to design and verify your design before it goes to the foundry. Although initially cell libraries and PDKs would have to be made by hand, enough graduate students came together across the world and we got an OpenSource PDK. But this is not truly OpenSource as it requires Cadence, about $5000/seat/month program to run (which is free to universities, of course). 
Due to that cost, a hobbyist group would probably be better off putting together the OpenSource RTL with a proprietary Foundry's cell library and PDK with some foundry-supported cheaper software. So much for the OpenSource PDKs.


So in short, OpenAnything is not new. As many other ideas, like the Internet or the web, it actually starts from academic collaborations that later became inclusive of the whole public and took a life of their own.

So no. They will not be the first.
And no. You cannot have "OpenSource ASICs." That simply does not make sense.

The Ethereum Foundation can simply do what all of us mere mortals do and grab and OpenSource RTL and load it into an FPGA. But that will not be an "ASIC."

The Ethereum Foundation can contact one of the many fabless houses or fabs that offers the full service of RTL-to-ASIC to do that part of the work for them, but that would not be "OpenSource."

But if that is not enough, here is some people that went all the way to ASIC, released what was basically a single hobbyist labor of love as a product, and then went back to FPGA so that it could actually be released as OpenSource. So no, they will not be the first.