As of 2022/03/01, bootsvc is no longer doing anything useful in the boot process besides loading component manager, and the flag //products/kernel_cmdline:userboot-next--skip_bootsvc exists to load component manager directly from userboot.
Any new business logic that you were intending to put in bootsvc likely belongs in component manager, or much less likely in userboot. If neither of these binaries satisfies your requirements, please reach out to dahastin@ and abdulla@. For the current status of the final deprecation and removal from the ZBI, see fxr/44784.