Bug#599417: also affects ia64
Note that ia64 also suffers from this artificial restriction because
the elilo.efi bootloader does not read files from the /boot directory.
Rather, these files are read from a separate disk partition - the EFI
partition - that is not mounted by the OS by default. The EFI
partition is updated by a kernel hook when boot files are changed. In
many ways this is similar to the flash-kernel case with the NVRAM
replaced by a disk partition.
It (perhaps naively) seems to me like the logical place to store this
data would be to have the individual bootloader installer packages
specify the list of filesystems from which they can boot, and have
partman disallow /boot to reside on a filesystem for which no
supportable bootloader is available.