Electronic – Features to include on a new embedded Linux board to make development and debug easier

I'd like to see this too, but my gut instinct is to say "maybe, but it's a lot of work". Even the smallest Linux distro is going to need around a megabyte of RAM to run. This means at least 30 or so additional pins for the RAM controller in the microcontroller, and a couple of big RAM chips.

One of the simplest architectures I know that has Linux for it is the Atmel AVR32 series of parts. The smallest, the AT32UC3A0128 comes in a relatively hacker-friendly 100-pin TQFP package. This is at least amenable to hand-soldering, unlike most of the OS-capable embedded microcontrollers that come in BGA packages. (the chips that have the little solder balls underneath them) You can get an idea as to the complexity of a circuit using that chip by examining the EVK1100 eval board.

Both the bootloader and Linux distribution depend on what your final application is.

RedBoot and uBoot are both popular bootloaders for embedded Linux. They support writing to flash, loading code over serial/ethernet etc. But, for a deeply embedded device, a very minimal loader might be better, leaving everything else to linux.

If you need access to a lot of software packages, you might try Debian's ARM port. For anything else, I'd recommend OpenEmbedded or Buildroot - both are configurable build systems for generating linux kernels and filesystems with only what you need and nothing else in.