Some among the cheaper boards are much less capable than the RPi4; 256 or 512 MB RAM can indeed run a tiny Linux desktop, but for some uses it would struggle for lack of resources. A single user system with no layers of code devoted to security (which would be pointless in non connected devices) would probably be a lot faster on constricted hardware. The goal of such a system shouldn't be to replace BSD or Linux, which do what they do extremely well, but to offer a smaller tinier system for those contexts when the basic functionalities of an OS are needed without the inevitable bloat that comes with security and support for beefier hardware and/or more complex software. "It couldn't run LibreOffice? Who cares! If I wanted to use it for that I'd use Linux instead."
I mean, If I want to build say a fully autonomous portable software defined radio that boots in a handful of seconds straight to its GUI on a very small board, I'd have a hard time doing that with a full Linux distro, no matter how optimized it is, since it still is a full UNIX-like OS with all the bells and whistles that would make it runnable on a supercomputer.
I think that those small OSes could potentially fill a gap between smaller things such as no OS at all or smaller ones such as FreeRTOS and complete Linux systems, but to really appreciate them they should also run on hardware such as ARM, RISC-V, etc.
I'm somewhat skeptical of the usefulness of 16 and 32 bit software : 8-bit is simple and can do ASCII, sRGB... while 64-bit is enough for the foreseeable future, but in-between ? You're just hampering yourself for dubious gains...
I mean, If I want to build say a fully autonomous portable software defined radio that boots in a handful of seconds straight to its GUI on a very small board, I'd have a hard time doing that with a full Linux distro, no matter how optimized it is, since it still is a full UNIX-like OS with all the bells and whistles that would make it runnable on a supercomputer. I think that those small OSes could potentially fill a gap between smaller things such as no OS at all or smaller ones such as FreeRTOS and complete Linux systems, but to really appreciate them they should also run on hardware such as ARM, RISC-V, etc.