I'm also very interested in this how to, specially because of the different toolchain available now. I think the firmware compilation process is clearly explained, even if it lacks info on how to add or modify things, it's enough to get started.
On the other side, they are multiple posts on how to compile a specific program, and most rely on using the correct toolchain, and modifying the makefile. Why should we use mipsel -linux or mipsel-uclib is still a mistery for me.
I think a few info would be enough, but at least something that is not an answer about a specific program would be enough.
I use teach any language using an Hello world kind of example. This is probably what's missing the most. maybe there can be 2 step, for program with standard library, and programs with specific library.
As an example, I tryed to compile netcat (the full one, not the busybox one) because there was no complex library involved. The compilation went fine, but the binary always give a -sh: ./netcat: not found
error message that I know is not a missing LD_LIBRARY_PATH problem.
I cannot help for making the technical part of the tutorial, but I can write things if they are explained brifly to me, and also help providing a roadmap for it.