There is already plenty of open hardware, it's just not this-year's-top-performance.

In the category of ~1-3 years' performance lag you get Rockchip and friends, which are closed hardware that allows open computation. See computers made by the company MNT as an example.

In the category of ~5 years' performance lag you get "soft" cores, where you buy an FPGA (dynamically reprogrammable hardware) and make it run a CPU you design yourself. If you want to, for example, make your CPU have more cache and fewer ALUs, you can do that by tweaking some files and reprogramming the FPGA. This has a cost in terms of power efficiency and runtime speed, but you can absolutely run a full Linux desktop experience on an FPGA today, and the hardware has no way to try to prevent you from running any software.

You can solve the problem of all the cellular basebands being closed source with either software-defined-radio or using a closed USB/PCIe cellular modem connected to an open processor.