Hi spavlin & nice work!
by editing the BCD you can try to run a different arm .efi executable like the efi shell for exemple.
but there is always the secure boot restriction!
PK:Platform Key (OEM)
KEK: Key Exchange Key ( From MS preload in db by oem's )
DBX: Revoked Signatures Database
DB: Allowed Signature Database
Platform Key controls which Key Exchange Keys can be enrolled,
and the Key Exchange Keys control which software is allowed to run.
The PK does also two things:
1- enrolling it is required to enable secure boot.
2- controls the enrolling of KEK keys
if secure boot is disable there are no restrictions on which KEKs may be enrolled
In order for software to boot it must be signed by an enrolled KEK.....
you can always try to run some arm efi extracted from rom,test rom or WinRT if
it's signed with non revoked signature....