@jwildeboer >but it never was Open Hardware
I don't get what "open hardware" is meant to mean, as source code doesn't pertain to physical objects: https://www.gnu.org/philosophy/free-hardware-designs.en.html

Not having the board design is an issue when it comes to repairs, but isn't always a problem software freedom wise.
The main problem with the many raspberry pi models currently isn't that the designs are proprietary, but that you can't use them without providing proprietary software.
There is a project which aims to replace all the proprietary things and is quite successful, but so far hasn't achieved full hardware support.

If full hardware support is achieved with all free software, then the main problem could then be the not having the board design.

>there is a huge opportunity to have a RISC-v based alternative to both Arduino and Raspberry. Who takes it?
"Alternative" implies that either the Arduino's or Raspberry Pi's are acceptable choices, did you mean replacement?

Arduino's actually aren't too bad - they publish the board design for most boards (not sure under what license), you can operate Arduino's without providing any proprietary *soft*ware and the AVR instruction set is simple and free of patents currently if I remember correctly.
They're pretty much excellent for anything 5V, but most things are 3.3V now sadly.

The RISC-V instruction set definition and example designs are all under free licenses, the problem is that most manufacturers go and add a bunch of proprietary extensions to the base instruction set and patent those extensions, thus managing to be worse than Aarch64 in most situations somehow.

A lot of RISC-V implementations have the problem of not being bootable without proprietary software as well.