Why do you let user-mode programs access the hardware directly?
You don't do this with network devices (there you have syscalls), you don't do this with sound devices (alsa).
Any root process can mmap() any of the memory-mapped hardware
including network devices. This isn't normally done because
handling interrupts from such hardware isn't very efficient
in user-mode, and redistributing data meant for another
process would be a nightmare. However, it can be done.
IMO it makes a proper power managment implementation impossible.
Wrong. The 'normal' user can't do such I/O, root can. See iopl(), which
sets the I/O privilege level. This has nothing to do with power-
management.
Last time I've tried a LiveCD distro I've seen a nice boot console with background picture, high resolution (1024x768) and nice small font. That means that the framebuffer driver had to be initialized at that time. I don't have framebuffer drivers compiled into my kernel so I don't know at which point these are initialized, but it must be at a quite early point in the boot process.
Even Fedora, which boots in a 'graphical' mode, really boots standard
text-mode until 'init' gets control. They just hide the console output
by setting the grub command-line parameter, "quiet".
The kernel messages are still available using `dmesg`. If you want
to eliminate any possibility of losing kernel messages because
the kernel failed to get up all the way, just use /dev/ttyS0 as
your console during boot.