I don't know how easy it would be to get a bootloader to call a D kernel although it has been done.
Pretty easy if you use GRUB. You can just compile a regular linux program with a linker script and load it right up.
My minimal.zip (a bit of a misnomer as it is more than minimal including some experimentation) has some code to run D on bare x86 metal
arsdnet.net/dcode/minimal.zip
