Trade-offs

Though this is starting to feel like we'll eventually need an extra stage of loading Linux. Eg:

Stage 1: Get to a bootloader. (Obviously there's earlier steps, but let's start here.)
Stage 2: Load Linux and initrd into memory. We need just enough in initrd to access some real storage in early userland.
Stage 3: Initrd loads further modules from storage, for things like LUKS passwords. Eventually loads root fs and boots to full userland.

Our forced-memory-resident initrd could be much smaller. Our big stage3 modules could live anywhere that Linux supports, instead of being reliant on the minimal filesystem drivers in bootloaders.