It's possible.
@Algernon-01 managed to implement it in @Whonix which is using grml-debootstrap. (https://github.com/Whonix/Whonix/pull/419)

In essence if I did not overlook something - deduction from theory (code reading):

• export DEBOOTSTRAP='qemu-debootstrap'
• export FSCK='no' (?) (Maybe @Algernon-01 can explain?)
• skip installation of grub (since it does not exist for that platform) - allow skip installation of grub #113
• packages ((https://github.com/Whonix/anon-meta-packages/pull/11)): rpi-patches, wpasupplicant, firmware-iwlwifi, firmware-atheros, firmware-brcm80211, firmware-ralink, firmware-realtek, iw, fake-hwclock
• parted, mkfs stuff as per 2375_build_rpi_fs

Would be cool if grml-debootstrap supported RPI out of the box.