Thanks for the suggestion. However, busybox-power itself won't need to be incepted. Nokia deployed, just like in Fremantle, a metapackage in Harmattan that depends on specific versions of system packages, including busybox.
That means we have to replace /bin/busybox in busybox-power's postinst to not break any (C)SSU updates while still being able to provide busybox-power updates via community repositories, just like busybox-power did in Fremantle.

Busybox-power for Harmattan will depend on inception/opensh and aegisctl though. It requires either inception (more specifically: ariadne) or opensh to replace /bin/busybox, update aegis' refhashlist, and resign the list.

Aegisctl is required to temporarily allow untrusted binaries to be executed. Aegis loads all reference hashes in the kernel when booting your device. This means that during the period between replacing /bin/busybox and the next reboot, access to /bin/busybox would otherwise be denied for root. That's highly undesirable of course, hence the dependency on aegisctl.